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1 June 2009 Phylogeny and Biogeography of Pholadid Bivalve Barnea (Anchomasa) with Considerations on the Phylogeny of Pholadoidea
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The paper examines the systematics, phylogeny and biogeographical history of Barnea (Anchomasa), which is one of the most abundant and diversified of modern pholadid bivalves. The range of morphology of its distinctive characters and comparisons with other pholadoidean taxa are described in detail. An extensive cladistic analysis based on morphological characters at genus and subgenus levels allowed the inclusion of B. (Anchomasa) into the phylogeny of Pholadoidea and the establishment of its most appropriate taxonomic position. The analysis confirms that Barnea s.s. and B. (Umitakea) are its closest relatives and that the morphological similarities to other taxa are mainly due to plesiomorphies. The fossil record and the data on the present-day distribution contributed to trace the biogeographical history of B. (Anchomasa). The present-day biogeography is marked by the disjunct distribution of species. Species are distributed mainly either along the Atlantic and Pacific coasts of the American continent (American group) or in the Indo-West Pacific region (Indo-West Pacific group). Both these groups have distinct morphological features and biogeographical structures. The fossil record and the known geodynamic scenario suggest a relationship of direct derivation between the Indo-West Pacific group and a stock of north-eastern Atlantic to Paratethyan species. This reflects a vicariant event related to the closure of the connection between western Tethys and the Indian Ocean in the middle Miocene. The American group presumably arose from the European stock during the Late Pliocene by dispersal towards the eastern coasts of North America and rapid southward diffusion. A relative differentiation within the American group is probably related to the last phases of emergence of the Panama Isthmus. The cladistic analysis also gives suggestions for the reconstruction of the phylogeny of the superfamily Pholadoidea. It confirms the interpretation of several characters sustained by previous authors. However, it also shows remarkable differences to the previous taxonomic arrangements. Pholadinae includes only taxa having the protoplax and it appears to be the sister-group of a major clade composed mainly of two groups, namely Martesiinae-Jouannetiinae and Xylophagainae—Teredinidae. The Martesiinae are paraphyletic whereas the obligate wood-boring Xylophagainae and Teredinidae form a well-supported monophyletic group.


The pholadoideans are a group of bivalves specialised for boring into a wide variety of substrates (Turner 1969). Their mode of life clearly reflects on a set of peculiar features of the shell and soft body which has attracted the attention of several authors (see for example Hoagland and Turner 1981 for a list of references and Turner 1998 for a short synthesis). Relevant characters are the truncate foot with discoid extremity adapted for suction and extended out of the shell through a narrow to very wide anterior gape, the outward reflection of the anterodorsal margin of the shell, forming the mostly external attachment area of the anterior adductor muscle, and the simplified hinge structure lacking teeth and with internal ligament small to absent. Other special features (for a list and descriptions see Turner 1969: N705) distinguish the different groups of pholadoideans, e.g., the accessory plates (protoplax, metaplax, mesoplax, hypoplax, and siphonoplax) for supplementary protection of the soft body, and the apophyses acting as structures for the insertion of the pedal muscles.

The major systematic arrangement proposed by Turner (1954, 1955, 1966, 1969) and subsequent authors (e.g., Vokes 1980; Amler 1999), subdivides the pholadoideans into two families, namely Pholadidae Lamarck, 1809 and Teredinidae Rafinesque, 1815. Several authors described their features and mode of life (see references in this paper and in Baker and Padilla 2004). The teredinids (shipworms) are characterised by having a strongly reduced shell and worm-like soft body, the burrow lined by a calcareous tube on which the siphonal retractors are inserted, and pallets closing the tube during the siphons' withdrawal. All the teredinids, apart from very few exceptions (Kuphus Guettard, 1770 and possibly some species of the genus Uperotus Guettard, 1770; Turner 1998), are obligate wood-borers. In fact, they utilise the wood for food and are provided with a wood-storing caecum in their alimentary apparatus. Furthermore, the presence of bacterial endosymbionts in the gills, allowing the digestion of cellulose, is ascertained in many species (Turner 1998 and references therein). In contrast to the teredinids, the great majority of Pholadidae (piddocks) are filter-feeders, namely the Pholadinae Lamarck, 1809, Jouannetiinae Tryon, 1862, and Martesiinae Grant and Gale, 1931. They bore into inorganic and organic substrates of variable hardness and, occasionally, into waterlogged and decayed wood. A few Martesiinae are almost exclusively wood-borers but they lack the wood-storing caecum and they filter-feed. The Xylophagainae Purchon, 1941 represent the only pholadid group of obligate wood-borers which differ from the other pholadids by living mainly in deep-sea environments.

This paper investigates the subgenus Barnea (Anchomasa) Leach, 1852, which is one of the most widespread and abundant pholadid taxa, including about fifteen living and fossil species. The taxon has a worldwide present-day distribution. The type species, Barnea (Anchomasa) parva (Pennant, 1777), occurs along the Atlantic coasts of the British Isles and France. A number of species are known from the Indo-West Pacific region and a few other species from the Atlantic and Pacific coasts of the American continent. Detailed analysis shows that the species living along the coasts of the American continent differ from the Indo-West Pacific species in having some distinctive characters (see details below). The present study attempts to understand the origin of that differentiation.

Institutional abbreviation.

  • MGPD, Geological and Palaeontological Museum of the Department of Geosciences, University of Padua, Italy.

Material and methods

As a first step a morphological analysis at species level was accomplished in order to identify the distinctive characters of B. (Anchomasa) and their variability, and to compare the subgenus with other pholadoidean taxa. The morphological study is founded on the critical examination of the data available either on the fossil species (Pennant 1777; Sowerby 1818; Dujardin 1837; Wood 1850, 1874; Fischer 1866; Nyst 1878–81; Dolfuss and Dautzenberg 1902; Merklin and Nevesskaya 1955; Zhizhchenko 1959; Gilbert 1963; Sakhelashvili 1965; Gilbert and Van de Poel 1966; Kennedy 1974; Janssen et al. 1984; Kensley and Pether 1986; Beu and Maxwell 1990; Nevesskaya et al. 1993; Beu 2006; Monari 2008 and references therein) and living species (Say 1822; Hedley 1893; Bartsch 1915; Carcelles 1944; Allan 1950; Nicklès 1950; Turner 1954; Purchon 1955; Phillips et al. 1984; Oliver 1992; Bosch et al. 1995; Ito 1998, 1999; Lamprell and Healy 1998; Poutiers 1998; Turner 1998; Higo et al. 1999; Robba et al. 2002), and on the analysis of the material deposited at MGPD.

A cladistic analysis at genus and subgenus levels was performed to establish the phylogenetic relationships of B. (Anchomasa) with the other pholadid taxa, to determine the origin of their similarities and differences, and to place the subgenus in the most appropriate taxonomic position. In order to obtain maximally reliable results, the analysis was extended to all the pholadoidean taxa supported by a sufficient amount of available data. The study is based on the rigorous selection of characters and taxa extracted from the contributions of previous authors and from personal observations. In particular, available data come from the following sources: Purchon (1941, 1955, 1987), Clench and Turner (1946), Fitch (1953), Turner (1954, 1955, 1961, 1962, 1966, 1969, 1972a, 1972b, 1998, 2002), Ansell and Nair (1969), Smith (1969), Röder (1977), Turner and McKoy (1979), Hoagland and Turner (1981), Savazzi (1982), Hoagland (1983), Wilson and Kennedy (1984), Okamoto and Habe (1987), Kelly (1988a), Kennedy and Armentrout (1989), Turner and Santhakumaran (1989), Evseev (1993), Pacaud (1998), and Lopes et al. (2000).

Such an extensive analysis provides suggestions also for the interpretation of the phylogeny of the whole superfamily. A discussion of the main results is given below, especially concerning the validity of the current systematic arrangement, the verification of the monophyletic composition of the families and subfamilies, and the significance of the characters of the shell for the reconstruction of the phylogeny of the pholadoideans.

The present-day distribution of B. (Anchomasa), which reveals the presence of different biogeographical groups, and critically revised data concerning the fossil record are used in relation to the geologic evolution of the regions concerned, allowing the biogeographical history of the subgenus to be elucidated. Finally, the characters distinctive of the different biogeographical groups were employed in a simple cladistic test of the hypotheses of historical biogeography.


Suborder Pholadina H. Adams and A. Adams, 1858
Superfamily Pholadoidea Lamarck, 1809
amily Pholadidae Lamarck, 1809
Subfamily Pholadinae Lamarck, 1809
Genus Barnea Leach in Risso, 1826
Subgenus Anchomasa Leach, 1852

  • Type species: Anchomasa pennantiana Leach, 1852 (a junior synonym of Pholas parva Pennant, 1777).

  • Characters and variability.—According to Turner (1954, 1969), B. (Anchomasa) belongs to the genus Barnea in having a simple (not septate) umbonal reflection and a single, anterodorsal accessory plate represented by the lanceolate, undivided and calcareous protoplax. Moreover, Barnea s.s. and B. (Anchomasa) share the presence of long and thin apophyses (Pacaud 1998). B. (Anchomasa) differs from Barnea s.s. in having a wide pedal gape (Turner 1954, 1969) and, consequently, well-defined prora (sensu Kelly 1988a).

    The main characters varying in B. (Anchomasa) are the general morphology of the shell, the position of the umbo and the shape of the posterior margin (Fig. 1). In most of the living species, the shape of the shell is elongate to tapered, with length clearly exceeding height. However, in the type species, B. (A.) parva (Fig. 1D), and in some fossil species, such as Barnea (Anchomasa) palmula (Dujardin, 1837) and Barnea (Anchomasa) dumortieri (Fischer, 1866), the shell is much shorter in the antero-posterior direction. A variably marked radial umbonal-ventral depression of the shell is often present in B. (A.) parva (Fig. 1D1) which is hardly visible or is absent in the other species.

    The umbo is variably displaced in anterior position. The outline of posterior margin is lanceolate to subtruncate. A subtruncate posterior margin is usually associated with a wide posterior gape. In contrast, species having a lanceolate posterior part of the shell commonly develop a narrow posterior gape. The pedal gape is always wide and oval in outline. However, the concavity of its margin is slightly variable and, consequently, the prora project to a varying degree. The dorsal condyle, which is formed by the internal protrusion of the umbo below the umbonal reflection, is small to strong. The robustness of the apophyses and their inclination with respect to the direction of the dorsal margin are relatively variable as well. The ornament is composed of radial alignments of imbrications. In most species, they are well-evident in the anterior slope, where they range from few, strong and well spaced, to numerous, dense and relatively feeble. They attenuate towards the posterior part, where they rarely persist.

    As described in detail below, the combination of some of these aspects of variability characterizes groups with distinct geographical distribution.

    Adults of B. (A.) parva lack the chondrophore and ligament (Purchon 1955) (Fig. 1D3). On the contrary, Barnea (Anchomasa) manilensis (Philippi, 1847) shows a prominent chondrophore in the early juvenile left valve becoming a spiny vestigial process in the adult shell (Ito 1998, 1999) (Fig. 1A4). A small left chondrophore and right resilifer occur also in adult specimens of Barnea (Anchomasa) obturamentum (Hedley, 1893) (Fig. 1B2, B4), Barnea (Anchomasa) truncata (Say, 1822) (Fig. 1C2, C4), and Barnea (Anchomasa) similis (Gray, 1835) (Suter 1913). Ito (1998) maintained that the left chondrophore, right resilifer and active internal ligament are present in the early post-larval shells of many pholadoideans and these features should be considered as plesiomorphies of the superfamily inherited from bivalves having a chondrophore only in the left valve. According to that author, during the adult growth these structures become vestigial or disappear in many species, but they can also persist in independent lineages by paedomorphosis of the first fibrous ligament. The phylogenetic analysis below confirms the ontogenetic plasticity of the chondrophore, which acts as a highly homoplasic character.

  • Comparisons.Barnea (Anchomasa) shows similarities with B. (Umitakea) Habe, 1952. Turner (1969) considered Habe's subgenus to be a junior synonym of B. (Anchomasa). On the contrary, Vokes (1980) treated B. (Umitakea) as a distinct taxon. Evseev (1993) deeply studied the type species, Barnea (Umitakea) japonica (Yokoyama, 1920) and compared it with B. (A.) parva, mainly based on the data published by Purchon (1955) and Turner (1954). Evseev (1993) listed some details of the anatomy of the soft body, e.g., the long caudal process of the visceral mass, the isometric and compressed ventricle and the morphology of the midgut, considered to be distinctive characters at supraspecific level. However, these characters are unknown in the other species of B. (Anchomasa). Thus, their supraspecific variability as yet can not be defined.

    Ito (1998, 1999) underlined that B. (U) japonica differs from B. (A.) manilensis in retaining a prominent chondrophore at the adult stage. As mentioned above, the adult chondrophore in B. (Anchomasa) is highly variable and in some species it is slightly less prominent than that illustrated by Evseev (1993) for B. (Umitakea). Differences based on that feature may not be valid to make distinction among these taxa.

    B. (Umitakea) differs from B. (Anchomasa) in characters of the general shape of the shell. They are evident in comparing the respective type species, although the overall variability of B. (Anchomasa) makes the differences less distinct. B. (Umitakea) has a much higher shell and the length to height ratio clearly exceeds the field of variability of B. (Anchomasa). The anteroventral margin is slightly concave to slightly convex and, consequently, the prora project less. Moreover, B. (Umitakea) has a much wider posterior gape (Evseev 1993).

    Barnea (Taiwanobarnea) Wang, 1983, from the late Miocene of Taiwan, shares with B. (Anchomasa) and B. (Umitakea) the presence of a wide pedal gape and an undivided, calcareous protoplax as a single accessory plate. The degree of the antero-posterior elongation of the shell is intermediate between B. (Anchomasa) and B. (Umitakea). However, the moderately prominent prora and the inflation of the anterior region of the shell would indicate closer affinities with B. (Umitakea). Furthermore, according to Wang (1983), the type species, Barnea (Taiwanobarnea) shihchoensis Wang, 1983 is very similar to B. (U.) japonica, differing in the convex outline of the anteroventral margin and in the absence of a spiny sculpture on the anterior part of the shell. However, as mentioned above, the slightly convex outline of the anteroventral margin is an aspect of the variability of B. (Umitakea) as well. Since the differences in the ornament pattern could be not sufficient alone to justify the institution of a distinct subgenus, B. (Taiwanobarnea) is strongly suspected to be a junior synonym of B. (Umitakea). These considerations and the lack of information on the internal shell characters determined the exclusion of B. (Taiwanobarnea) from the cladistic analysis below.

    B. (Anchomasa) is also very similar to Cyrtopleuropsis Pacaud, 1998. In fact, the ranges of variation in the shape of the shell, the outline of the anterior area and the ornament are widely continuous among the two taxa. Moreover, as discussed above, the presence of the chondrophore, which Pacaud (1998) included in the diagnostic features of Cyrtopleuropsis, is not useful for distinguishing Pacaud's genus from B. (Anchomasa). Cyrtopleuropsis differs from B. (Anchomasa) in having wide and spoon-shaped apophyses and the posterior slope ornamented by granulations. Accessory plates of Cyrtopleuropsis are unknown.

    B. (A.) parva has general similarities with Nipponopholas satoi Okamoto and Habe, 1987, type species of Nipponopholas Okamoto and Habe, 1987 and with the species belonging to the genus Zirfaea Leach in Gray, 1842. However, in Nipponopholas and Zirfaea the single accessory plate is represented by the mesoplax. Furthermore, Zirfaea has a ventral condyle and an internal umbonal-ventral ridge corresponding to an external sulcus. However, in the fully adult shells of Zirfaea crispata (Linnaeus, 1758) these features become reduced (Turner, 1954) and an evident internal radial ridge and ventral condyle are present in the early juvenile shells of B. (A.) manilensis, but disappear completely during adult growth (Ito 1999).

  • Fig. 1.

    Variability of pholadoidean bivalve Barnea (Anchomasa) Leach, 1852. A. Barnea (Anchomasa) manilensis (Philippi, 1847), Recent, Natal, Durban Bay, South Africa; MGPD30087b, external view of left valve (A1), and detail of the umbonal region showing the chondrophore (A2); MGPD30087a, internal view of right valve (A3), and detail of umbonal region showing the resilifer (A4). B. Barnea (Anchomasa) obturamentum (Hedley, 1893), Recent, Largs Bay, South Australia; MGPD30089b, external view of right valve (B1), and detail of the umbonal region showing the resilifer (B2); MGPD30089a, internal view of left valve (B3), and detail of umbonal region showing the chondrophore (B4), apophysis not preserved. C. Barnea (Anchomasa) truncata (Say, 1822), Recent, Suffolk Country, New York; MGPD30092b, external view of left valve (C1) and detail of the umbonal region showing the chondrophore (C2); MGPD30092a, internal view of right valve (C3) and detail of umbonal region showing the resilifer (C4). D. Barnea (Anchomasa) parva (Pennant, 1777), Recent, Bristol Channel, England; MGPD30091b, external view of right valve (D1); MGPD30091a, internal view of left valve (D2) and detail of umbonal region showing the absence of chondrophore (D3), apophysis not preserved.


    Phylogenetic analysis

    Characters.—The selection of characters (Appendix 1) started from the analysis of the list at species level made by Hoagland (1983), on which Hoagland and Turner (1981) based their phenetic analysis. Among the characters indicated by these authors, only features showing a sufficiently homogeneous distribution at genus and subgenus levels were considered. Then, the list was upgraded and completed by the inclusion of data coming from other sources (see above for references). Most of the characters are features of the shell and accessory structures. The aspects of the soft body were included mainly to ensure a balanced evaluation of the Teredinidae.

    The main constraints are exerted by the scarcity of information on the ontogenetic changes of the selected characters. Furthermore, some aspects of the soft body, which previous authors (e.g., Purchon 1955; Evseev 1993) presumed to be significant at supraspecific level on the basis of comparisons among few species, were excluded from the analysis. These characters lack information on a sufficient number of species and this prevents verification of their validity at genus and subgenus levels.

    The definition of morphological terms are mainly those established by Turner (1954, 1955, 1966, 1969, 2002) with the emendation made by Kelly (1988a) suggesting the term “prora” as a replacement for “anterior beak”. In the matrix (Appendix 2), characters depending on the states of other characters are codified as not-applicable (N), but processed as missing data identified by “?”. Autoapomorphies were excluded from the list of characters and the matrix.

    Taxa.—Selection of taxa was based on the list of genera and subgenera ascribed by Turner (1954, 1955, 1966, 1969) to the Pholadoidea, with the addition of B. (Umitakea), Cyrtopleuropsis, and Nipponopholas. Furthermore, Netastoma Carpenter, 1864 has been used in place of Nettastomella Carpenter, 1865 (Vokes 1980: 190). From Turner's (1969) list, only living and fossil taxa supported by a sufficient amount of information on the selected characters are included in the analysis. Most of the genera added by Vokes (1980) in the list of valid taxa lack that requirement.

    As far as the Teredinidae is concerned, several characters indicated by Hoagland and Turner (1981) and Hoagland (1983) as exclusive to that group were not considered here. Only a number of teredinid genera are included which cover the whole range of morphological diversity in the context of the selected characters. Further inclusions would have added taxa with coding already present in the matrix. For this reason, the relationships among the teredinid genera resulting from the present study may not be indicative of the internal subdivision of the family which should be tested by a more detailed subset analysis.

    Outgroup.—The selection of the outgroup is mainly based on the molecular phylogenetic analyses recently presented by Giribet and Distel (2003) and Taylor et al. (2007). Giribet and Distel (2003: 81) found that the family Sphaeriidae Deshayes, 1854 tends to be the sister-group of a clade including the Pholadinae, Xylophagainae, Teredinidae, Myidae Lamarck, 1809, Corbulidae Lamarck, 1818, Dreissenidae Gray, 1840, Mactridae Lamarck, 1809, and Ungulinidae H. Adams and A. Adams, 1857. Moreover, the pholadoideans are polyphyletic and included in a monophyletic group together with the Myidae, Corbulidae, and Dreissenidae (Giribet and Distel 2003: 82). According to Taylor et al. (2007), the Sphaeriidae are the sister-group of a clade composed of Pholadidae, Teredinidae, Dreissenidae, Myidae, and Corbulidae. The Pholadidae and Teredinidae are in paraphyletic relationships. Thus, Sphaerium Scopoli, 1777 (Sphaeriidae) was selected as outgroup. In addition, two myoidean taxa were included in the matrix, namely Mya (Arenomya) Winckworth, 1930 (Myidae) and Corbula Bruguière, 1797 (Corbulidae). The analysis of their characters is mainly based on personal observations and on information contained in the following sources. Data on Sphaerium were extracted from Keen and Dance (1969), Castagnolo et al. (1980), Lee (2001), Giribet and Wheeler (2002), and Korniushin and Glaubrecht (2002). Data sources on Mya (Arenomya) come from Yonge (1923), Pumphrey (1938), Fitch (1953), Keen (1969), Purchon (1987), and Giribet and Wheeler (2002). Anderson and Roopnarine (2003) and Keen (1969) supplied information for Corbula.

    Method.—The data matrix is composed of 39 taxa and 47 characters (Appendix 2). A heuristic search, with random addition sequence of 100 replicates and TBR branch-swapping algorithm, was performed employing Paup 4.0b10 (updated version of PAUP 4.0 beta version; Swofford 1998). Characters were treated as unordered and equally weighted, and changes of character states were optimised under both ACCTRAN and DELTRAN conditions. Trees were rooted using the default outgroup (Sphaerium). Rooting by inclusion of Mya (Arenomya) and Corbula into the outgroup produced the same ingroup trees. Then, the analysis by successive approximation reweighting, using characters weighted by maximum values of rescaled consistency index, was performed under the same search setting as that of the unweighted search. The bootstrap method under weighted conditions supplied the support values for clades. The resultant extremely long computational bootstrap time, was reduced by imposing a limit of 1000 replicates and 10000 maximum trees retained per replicate. These constraints were established by increasing gradually both the number of replicate and maximum trees up to the stabilisation of the bootstrap tree and support values.

    Fig. 2.

    Phylogeny of Pholadoidea. A. Strict consensus tree obtained by heuristic search with unordered and equally weighted characters. B. Strict consensus of 173 most parsimonious cladograms retained by successive approximation weighting.


    Results.—The unweighted heuristic search found 3192 maximally parsimonious cladograms [length (L) 96, consistency index (CI) 0.54, retention index (RI) 0.85, rescaled consistency index (RC) 0.46]. The strict consensus is shown in Fig. 2A. The reweighting drastically reduced the number of most parsimonious cladograms. It retained 173 cladograms (CI 0.78, RI 0.94, RC 0.74), all included in the most parsimonious cladograms obtained by the unweighted search. The strict consensus tree (Fig. 2B) retains the ingroup node and all the internal nodes of the unweighted strict consensus tree.

    As underlined by Smith (1994), consensus trees are arbitrary and conventional solutions. However, the Majority Rule consensus tree obtained by the analysis (Fig. 3) corresponds to one of the most parsimonious cladograms. Thus, that cladogram is maintained as the most probable representative of the phylogeny of the superfamily under the assumptions and list of characters here considered.

    In contrast with the analyses of Giribet and Distel (2003) and Taylor et al. (2007), the Pholadoidea result to be a monophyletic group. They are organised in clades which partly correspond to the major taxa established by Turner (1954, 1955, 1966, 1969). B. (Anchomasa) belongs to a restricted clade of Pholadinae, composed only of taxa sharing the presence of a protoplax (character 24), which is the exclusive synapomorphy of that group. The absence of protoplax in Talona Gray, 1842 and Zirfaea, taxa ascribed by Turner (1969) to the subfamily Pholadinae, and in Nipponopholas determines their exclusion from that clade.

    Barnea s.s., B. (Anchomasai and B. (Umitakea) form a distinct clade (Fig. 4), although barely supported by the bootstrap. This is the sister-group of a clade gathering taxa characterised by large, spoon-shaped to spatulate apophyses (character 16), namely Pholas Linnaeus, 1758, Cyrtopleuropsis and Cyrtopleura Tryon, 1862. The arrangement of the Pholadinae clade and the distribution of the character states are in accordance with the suggestions given by previous authors concerning the taxonomic repartition and affinities of the taxa involved. In fact, the Pholas clade is consistent with Turner's (1954, 1969) subdivision into three subgenera: Pholas s.s., Pholas (Thovana) Gray, 1847 ana Pholas (Monothyra) Tryon, 1862. These taxa share the septate umbonal reflection (character 6), which is an exclusive synapomorphy, and the presence of a metaplax (character 30). The composition of the CyrtopleuraCyrtopleuropsis clade, gathering taxa with the umbonal reflection free, raised and square at its posterior end (character 8), is in agreement with the suggestions expressed by Pacaud (1998) who recognised close the relationship of Cyrtopleuropsis with Cyrtopleura s.s. and Cyrtopleura (Scobinopholas) Grant and Gale, 1931. Furthermore, each internal clade of Pholadinae contains taxa with a narrow pedal gape besides taxa with a broad pedal gape (character 13). This is consistent with Turner's (1954, 1969) interpretation in attributing subgeneric rank to the shape of the pedal gape in the Pholadinae.

    Fig. 3.

    Phylogeny of Pholadoidea. Most parsimonious tree corresponding to the 50% Majority Rule consensus tree obtained by successive approximation weighting. L 96. Indices under unitary weight conditions: CI 0.54, RI 0.85, RC 0.46. Indices under reweight conditions: CI 0.78, RI 0.94, RC 0.74. Abbreviations: L, length; CI, consistency index; RI, retention index; RC, rescaled consistency index. Numbers in bold indicate the Majority Rule values and, in brackets, the bootstrap support values of the individual nodes. Only bootstrap values higher than 40% are shown. Numbers in smaller type represent the most significant state changes at the respective nodes. Exclusive synapomorphies are in bold. Unambiguous not-exclusive synapomorphies are in normal type. Abbreviations A and D mark the ambiguous changes of character states under ACCTRAN and DELTRAN optimisations, respectively. For changes of character states in the Pholadinae clade see Fig. 4. The classification of Pholadoidea in Turner (1969) is shown besides the tree by comparison.


    Fig. 4.

    Detail of the selected cladogram showing the relationships and state changes among the genera and subgenera of the Pholadinae clade. Symbols as in Fig. 3.


    Members of the Barnea clade are characterised by possessing thin apophyses (character 16) and in lacking the mesoplax (character 27). The presence of a mesoplax is treated as a plesiomorphy of the Pholadoidea that is independently lost in the Barnea clade, in Jouannetia (Jouannetia) DesMoulins, 1828, in Netastoma, and in the Teredinidae. The taxonomic position of B. (Anchomasa) as a subgenus of Barnea is in accordance with the results of the phylogenetic analysis, although the internal relationships among the taxa composing the Barnea clade are not resolved. The analysis shows also that similarities between B. (Anchomasa) and Cyrtopleuropsis, concerning characters of the general shape of the shell and the presence of a wide pedal gape, are plesiomorphies whereas the spatulate shape of the apophyses is a distinctive character placing Cyrtopleuropsis in a different clade within the Pholadinae. The relationships of B. (Anchomasa) to Nipponopholas and Zirfaea are more distant. As mentioned above, both these genera are excluded from the Pholadinae clade by lacking the protoplax. The presence of the umbonal-ventral ridge on the internal surface of the valves (character 17) and the presence of the ventral condyle (character 19) relates Zirfaea more closely to the sister-group of the Pholadinae.

    Phylogeny of Pholadoidea

    Cladistic analysis confirms the interpretation of numerous characters sustained by Hoagland and Turner (1981) and the gross topology of the cladogram recalls that obtained by them (Hoagland and Turner 1981: text-fig. 5, tab. 11) (Fig. 5) using the characters presumed to be unique and unreversed. In fact, the most consistent characters selected by the reweighting process are indeed those indicated by Hoagland and Turner (1981) as highly significant for the phylogeny of pholadoideans. However, the analysis at genus and subgenus levels shows remarkable differences. These are evident in comparing the structure of the selected cladogram with Turner's (1969) taxonomic arrangement (Fig. 3). Furthermore, it suggests that obscure areas of the phylogeny deserve further research.

    Exclusive synapomorphies supporting the ingroup node are represented by the presence of the umbonal reflection (character 5), the position of the umbo located well to the anterior (character 3), the cylindrical shape of the foot with discoid extremity adapted for suction (character 38), and the presence of imbrications on the commarginal ridges of the anterior slope (character 10), changing to fine denticulations in the wood-boring groups. The presence of apophyses (character 15) and the long ctenidia (character 41) are also important characters showing significant reversals in the ingroup (see below).

    The subfamilies Pholadinae and Martesiinae (sensu Turner, 1969) are not monophyletic. As described above, a monophyletic group of Pholadinae is exclusively composed of taxa having the protoplax. The Pholadinae clade is the sister-group of a major clade consisting of taxa having the umbonal-ventral ridge (character 17) and ventral condyle (character 19), the latter secondarily lost in Jouannetia.

    The major clade includes two groups, namely Martesiinae—Jouannetiinae and Xylophagainae—Teredinidae. The Martesiinae—Jouannetiinae clade is well-supported by two exclusive synapomorphies, i.e., the presence of the callum closing the pedal gape (character 21) and the consequent atrophy of the adult foot (character 37). However, the Jouannetiinae are monophyletic and well-supported by Majority Rule and bootstrap values, whereas the Martesiinae are paraphyletic. In fact, Martesiinae lack synapomorphies. The states of the characters differentiating the Martesiinae from Jouannetiinae, i.e., the presence of the apophyses (character 15) and the long ctenidia (character 41), are plesiomorphies of the Pholadoidea undergoing reversals in the Jouannetiinae. The Martesiinae—Jouannetiinae clade is subdivided in two main groups, one characterised by the presence of a hypoplax (character 31) and the other, including Jouannetiinae, having the siphonoplax (character 32) as a distinctive character.

    Fig. 5.

    Phylogenetic reconstruction of Pholadoidea and most significant state changes proposed by Hoagland and Turner (1981: tab. 11, text-fig. 5).


    According to Haga and Kase (2007), the Xylophagainae are phylogenetically distant from the Teredinidae and, consequently, the symbiosis with xylotrophic bacteria arose independently in these groups. On the contrary, the present study shows that the Xylophagainae and Teredinidae form a well-supported monophyletic group. This corresponds to the results of the molecular analysis made by Giribet and Distel (2003) in which Bankia Gray, 1842 is the sister-group of Xylophaga Turton, 1822. Thus, the position of Xylophagainae as a subfamily of Pholadidae as proposed by Turner (1955, 1969), is not justified. Exclusive synapomorphies are the gills beyond the posterior adductor (character 40) and composed of a single demibranch (character 39). The Xylophagainae lose the apophyses (character 15) independently from the Jouannetiinae.

    The structure of the cladogram here selected is in accordance with Hoagland and Turner's (1981) opinion in showing that the obligate wood-borers originated from the groups boring into inorganic substrates. However, a parallel evolution of the wood-boring adaptation in the Xylophagainae and Teredinidae cannot be excluded. In fact, the wood-storing caecum (character 45), which is commonly considered as the most important character reflecting the ability of wood-boring groups to use the wood for food (Purchon 1941; Hoagland and Turner 1981), is an ambiguous synapomorphy. In ACCTRAN optimisation it is a synapomorphy of the Xylophagainae-Teredinidae group which is secondarily lost in Kuphus. This would support a monophyletic origin of the xylotrophy in the pholadoideans. Alternatively, DELTRAN optimisation treats the character as originating independently in the Xylophagainae and in the Teredininae—Bankiinae clades. In this case, the absence of a wood-storing caecum and, possibly, the filter-feeding and mud-boring mode of life of Kuphus are plesiomorphies inherited from the ancestors of the obligate wood-boring groups.

    Insofar as the origin of the filter-feeding wood-borers is concerned, Ito (1999) and Haga and Kase (2007) maintained that the anterior boring mechanism of the rock- and wood-borers is primary and the groups with ventral boring mechanisms (sand- and mud-borers) evolved later. This hypothesis is supported by the fossil record which testifies that the wood-borers Opertochasma Stephenson, 1952 and Turnus Gabb, 1864 are the oldest pholadoideans known (Tithonian; Kelly 1988a, 1988b). According to Haga and Kase (2007), the highly specialised wood-boring groups are the most archaic pholadoideans and the great diversification of the superfamily originated by simplification of the shell morphology. On the contrary, the present analysis indicates that the filter-feeding wood-borers are the most derivative members of two Martesiinae clades. This represents a more parsimonious scenario of the evolutionary pathways of the pholadoideans in which the specialised forms, characterised by a high number of strongly adaptive apomorphies, arose from groups with a more generalist mode of life. As expected, the characters reflecting the adaptation to the wood-boring mode of life, i.e., the finely denticulate ornament of the anterior slope, the small and auricle-like prora giving the shape of an angulate embayment to the wide pedal gape, and the robust ventral condyle (Hoagland and Turner, 1981) developed independently in the Martesiinae clades and in the obligate wood-boring groups. As underlined by Kelly (1988a), the incompleteness of the fossil record and the lack of detailed studies on some problematic taxa do preclude definitive answers.

    The biogeographical history of Barnea (Anchomasa)

    Fossil record.—Turner (1969) maintained that the occurrence of B. (Anchomasa) dates from the Pliocene. However, Kennedy (1993) described Barnea (Anchomasa) saulae Kennedy, 1993 from early oniacian—Santonian of California, and assigned Pholas? scaphoides Stephenson, 1952, from Cenomanian deposits of Texas, to the subgenus B. (Anchomasa). Kelly (1988a) tentatively ascribed Stephenson's species to P. (Monothyra), presumably on the basis of the external shell characters. Pacaud (1998) maintained that the general shell shape and the ornament pattern recall also those of Cyrtopleuropsis. The Cretaceous species clearly show a simple umbonal reflection (Kennedy 1993). This would exclude their membership of the genus Pholas. Insofar as their relationships with B. (Anchomasa) and Cyrtopleuropsis are concerned, the only observable element of comparison is the abrupt interruption of the radial ornament along the line of demarcation of the disc with the posterior slope. This is a characteristic aspect of the ornament pattern of Cyrtopleuropsis, whereas it is unusual in B. (Anchomasa), in which the disappearance of the radial ornament in the posterior part of the shell is commonly gradual. In agreement with Pacaud's (1998) opinion, the genus attribution remains uncertain due to the lack of information on the internal features of the shell, particularly the morphology of the apophyses. The absence of data on the accessory plates of both these species and Cyrtopleuropsis is a further element of uncertainty. According to Kelly (1988a), P.? scaphoides could represent the most ancient fossil record of the subfamily Pholadinae.

    The oldest species showing the diagnostic characters of the shell of B. (Anchomasa) well come from the Miocene deposits of the Eastern Paratethys and France (Figs. 6, 7). These species constitute an ancient stock that, as explained below, seems to have had great importance for the biogeographical evolution of the subgenus. Barnea (Anchomasa) ujratamica Osipov, 1932 is known from the early Tarkhanian to Konkian (late Burdigalian to early Serravallian in Studencka et al.'s 1998 time correlation chart; earliest Langhian to early Serravallian in Harzhauser and Piller's 2007 time correlation chart) of a Paratethyan area extended from Crimea to Ustjurt (Osipov 1932; Merklin and Nevesskaya 1955; Zhizhchenko 1959; Sakhelashvili 1965; Gilbert and Van de Poel 1966; Nevesskaya et al. 1993; Studencka et al. 1998). B. (A.) palmula (Fig. 6A) occurs in the Pontilevian facies of Touraine (Loire basin) (Dujardin 1837; Dolfuss and Dautzenberg 1902; Gilbert and Van de Poel 1966) considered to be Langhian in age (Chaix and Cahuzac 2005 and references therein). Doderlein (1862) quoted the presence of the species also in the late Miocene of the northern Apennines (central Italy) but this information needs confirmation (Sacco 1901). B. (A.) dumortieri (Fig. 6B) is another western European species known from middle Miocene marine to fresh-water sediments constituting the uppermost part of the Cainozoic succession of the Rhone region (Fischer 1866; Locard 1878). These sediments should correspond to the Serravallian units of the southern part of the Bresse graben described by Sissingh (1998).

    Fig. 6.

    Fossil species of pholadoidean bivalve Barnea (Anchomasa) Leach, 1852 belonging to the European stock. A. Barnea (Anchomasa) palmula (Dujardin, 1837), from Dolfuss and Dautzenberg (1902: 58, pl. 1: 18–21), Langhian, Touraine, France. B. Barnea (Anchomasa) dumortieri (Fischer, 1866), from Fischer (1866: pl. 4: 3, 3a), middle Miocene, Rhone basin, France. C, D. Barnea (Anchomasa) parva (Pennant, 1777). C. From Janssen et al. (1984: pl. 91: 228a, b), Middle Pliocene, Netherlands. D. From Monari (2008: figs. 3a, b), Pleistocene, southern Tuscany, Italy. E. Barnea (Anchomasa) cylindrica (Sowerby, 1818), from Wood (1850: 295, pl. 30: 8a, b), Late Pliocene, England. Scale bars 10 mm.


    Fig. 7.

    Palaeogeographical distribution of pholadoidean bivalve Barnea (Anchomasa) Leach, 1852 during the middle Miocene. Map redrawn from Rögl (1998), Langhian. See text for sources.


    Concerning younger species of the western European region, Barnea (Anchomasa) cylindrica (Sowerby, 1818) (Fig. 6E) occurs in the Middle and Late Pliocene of England (Sowerby 1818; Wood 1850, 1874; Gilbert and Van de Poel 1966). Nyst (1843) mentioned very poorly-preserved specimens from Cainozoic deposits of Belgium which he doubtfully ascribed to Sowerby's species. B. (A.) parva is present in the Middle to Late Pliocene of England (Gilbert and Van de Poel 1966; Wood 1874), in the Early to Middle Pliocene of Belgium (Gilbert 1963; Nyst 1878–81) (Fig. 6C) and in the Middle Pliocene of Netherlands (Janssen et al. 1984). The presence of the species is quoted also in the Pleistocene of southern Tuscany (central Italy) (Monari 2008) (Fig. 6D). B. (A.) parva is the only member of the ancient European stock surviving today.

    Insofar as the north-western Atlantic region is concerned, B. (A.) truncata occurs in the Pleistocene in South Carolina (Dall 1898). The presence of the species in deposits of the same age on the western coast of South Africa (Kensley and Pether 1986 and reference therein) would contradict Turner's (1954) opinion that the species was recently introduced into western Africa. Moreover, this would indicate that the very wide present-day distribution of B. (A.) truncata (see below) was already accomplished in Pleistocene times.

    In the north-eastern Pacific area, Barnea (Anchomasa) subtruncata (Sowerby, 1834) occurs in the Pleistocene of California (Kennedy 1974).

    It is plausible that the specimens on which Noetling (1901) instituted Pholas blanfordianus Noetling, 1901, from the Miocene of the Burma region (Myanmar) and those ascribed by Hayasaka (1969) to B. (A.) aff. manilensis, from the Miocene of Tanegashima (south-western Japan), may represent the first occurrences of the subgenus in the western Pacific region. P. blanfordianus lacks information on the internal characters of the shell, on the morphology of the umbonal reflection and on the accessory plates, but its general shell shape is close to that of B. (Anchomasa). Its exact stratigraphical position is uncertain. A comparison between the stratigraphical subdivision of the Miocene of Burma made by Noetling (1901) and that currently in use (e.g., Khin and Myitta 1999, Wandrey 2006) permits only to infer that the species comes from the lower to middle Miocene marine and brackish water sediments below the Irrawaddy Group (upper Miocene to Pleistocene). As far as B. (A.) aff. manilensis is concerned, the deposits yielding the species belong to the Osaki Formation, i.e., the uppermost unit of the middle Miocene Kukinaga Group (Hayasaka 1969; Kodama et al. 1991; Inoue 2007 and references therein).

    The subgenus is certainly present in the late Miocene of New Zealand, with the specimens listed by Gregg (1960) as Barnea (Anchomasa) sp. and those listed by Suter (1921) as B. (A.) similis, the species living today along New Zealand coasts. Marwick (1931) and Keyes (1972) quoted the subgenus also in Lower Pliocene sediments. Beu and Maxwell (1990) maintained that B. (A.) similis is present from the Mangapanian (latest Pliocene) whereas the Early Pliocene specimens belong to a different, undescribed species. However, recently Beu (2006) extensively revised the systematic and stratigraphical data and highlighted the clear morphological continuity between the late Miocene and Recent material. According to Beu (2006), B. (A.) similis is a long-ranging species that first appeared in the late Tongaporutuan—Kapitean time span (late Miocene).

    Fig. 8.

    Present-day geographical distribution of pholadoidean bivalve Barnea (Anchomasa) Leach, 1852. See text for sources. A. Barnea (Anchomasa) alfredensis (Bartsch, 1915). D. Barnea (Anchomasa) davidi (Deshayes, 1874). E. Barnea (Anchomasa) erythraea (Gray, 1851). L. Barnea (Anchomasa) lamellosa (d'Orbigny, 1846). M. Barnea (Anchomasa) manilensis (Philippi, 1847). O. Barnea (Anchomasa) obturamentum (Hedley, 1893). P. Barnea (Anchomasa) parva (Pennant, 1777). S. Barnea (Anchomasa) similis (Gray, 1835). St. Barnea (Anchomasa) subtruncata (Sowerby, 1834). T. Barnea (Anchomasa) truncata (Say, 1822).


    Finally, B. (A.) manilensis is quoted in the Pliocene deposits of Japan and Korea (Yokoyama 1920; Kikuchi et al. 1991; Robbaetal.2002).

    Biogeographical distribution.—The subgenus B. (Anchomasa) has a worldwide present-day distribution, which is particularly accentuated in the western Pacific region (Fig. 8). The type species, B. (A.) parva, is diffused along the eastern coasts of the northern Atlantic region, from the British Isles to the Bay of Biscay (see details in Monari 2008) and it is also quoted in the westernmost part of the Mediterranean Sea (Pallary 1900).

    Apart from the type species, the global biogeographical pattern of the subgenus shows a disjunct distribution. This consists of two groups of species, here named the “American group” and the “Indo-West Pacific group” having distinctive morphological features. They have distinct biogeographical structures as well, which are revealed by the different ratio between widespread and local species.

    The American group is composed of the following species: B. (A.) truncata, B. (A.) subtruncata and Barnea (Anchomasa) lamellosa (d'Orbigny, 1846), sharing the truncate to subtruncate shape of the posterior margin (Fig. 1C). Moreover, the umbo is at almost one third of the shell length and the length/height ratio of the shell is commonly lower than that of the species of the Indo-West Pacific group. B. (A.) truncata and B. (A.) subtruncata show a very wide latitudinal distribution. They occur along the Atlantic and Pacific coasts of North and South America, respectively, from the boreal to austral temperate belts (Abbott 1954; Turner 1954; Keen 1958). B. (A.) truncata is also quoted along the central and southern Atlantic coasts of the African continent, from Senegal to Cape Twon (South Africa) (Nicklès 1950, 1955; Kensley and Pether 1986). On the contrary, B. (A.) lamellosa has a distribution limited to the coasts of Uruguay and Argentina (d'Orbigny 1846; Carcelles 1944; Turner 1954; Scarabino 2003).

    The wide distribution of these species is most probably determined by their relatively long planktonic larval life (Turner 1954; Chanley 1965), the capability of adaptation to different types of substrata and a certain tolerance to a wide range of temperature. Moreover, the spatial continuity of the shallow neritic areas along both the Atlantic and eastern Pacific coasts is an important aspect which contributed to greatly increase the dispersal of several marine groups in these areas (see for example Williams and Reid 2004).

    The Indo-West Pacific group consists of species having a tapered shell shape, a lanceolate posterior area and the umbo placed well anterior, at almost one fourth of the shell length (Fig. 1A, 1B). B. (A.) manilensis is the only widespread species of the Indo-West Pacific group, extending from the north-eastern coasts of South Africa to Japan (Bernard et al. 1993; Bosch et al. 1995; Poutiers 1998; Higo et al. 1999; Robba et al. 2002). The other relatively numerous species have limited distributions. Barnea (Anchomasa) davidi (Deshayes, 1874) occurs from the Bohai Sea to Taiwan (Deshayes 1874; Bernard et al. 1993; Higo et al. 1999). B. (A.) obturamentum lives along the southern coasts of Australia, from southern Western Australia to New South Wales and Tasmania (Hedley 1893; Allan 1950; Phillips et al. 1984; Lamprell and Healy 1998; Turner 1998), and B. (A.) similis is an endemic New Zealand species (Beu 2006 and references therein). The distribution of Barnea (Anchomasa) erythraea (Gray, 1851) is confined to the Red Sea (Oliver 1992). Barnea (Anchomasa) alfredensis (Bartsch, 1915) lives along the southernmost coasts of South Africa (Bartsch 1915).

    The high local vs. widespread species ratio makes the biogeographical structure of the Indo-West Pacific group clearly different from that of the American group. This pattern is the effect of different factors. Insofar as the western Pacific species are concerned, the radiation involved an area mainly composed of islands and archipelagos fragmenting the continuity of the shallow marine areas (Williams and Reid 2004). Moreover, the Late Cainozoic intense active margin tectonics, and the glacio-eustatic fluctuations (see Stevens 1994 for a synthesis) rendered this area strongly dynamic and contributed to increase the potential of isolation and speciation.

    Historical biogeography.—The origin of the disjunct distribution and the paths of radiation and dispersal of B. (Anchomasa) are not unequivocally discernible due to the time and space discontinuity of the fossil record. In spite of this, the following hypotheses could be considered which are in the best agreement with the available data.

    Lines of evidence suggest relationships of vicariance of the Indo-West Pacific group with the Eastern Paratethyan species as an effect of the dispersion before the closure of the connections between the Mediterranean—Paratethyan area and the Indian region during the Miocene. As a matter of fact, B. (A.) ujratamica shows morphological features characterising the species of the Indo-West Pacific group, i.e., a markedly anterior umbo and a lanceolate and elongated posterior area of the shell.

    As highlighted by phylogeographical studies (see Williams and Reid 2004 for a synthesis), the Tethyan closure was decisive for the origin of numerous marine Indo-Pacific taxa. Moreover, faunal comparisons (Robba 1987; Piccoli et al. 1991; Piccoli 2002) testify that the wide sea corridors linking these regions (the “Arabian gates” in Vrielynck et al. 1997) became strongly reduced or closed at the end of early Miocene time. Successive temporary connections were robust enough to allow interchanges (Franco 1982; Robba 1987; Piccoli 2002), particularly during the Langhian times (Rögl 1998, 1999; Studencka et al. 1998; Harzhauser and Piller 2007).

    According to the fossil record, the appearance of B. (A.) ujratamica dates back to the late early Miocene to earliest middle Miocene time span, whereas the most ancient members of the Indo-West Pacific group probably occur in the late middle Miocene of Japan and, certainly, in the late Miocene of New Zealand. This suggests that the Indo-West Pacific group originated from the Paratethyan species, although data on the occurrence of B. (Anchomasa) in the intermediate regions are currently lacking. However, the uncertainties mentioned above, concerning the age of P. blanfordianus and its membership of the genus B. (Anchomasa), leave open the possibility that the derivation took place in an opposite direction.

    The origin of B. (A.) erythraea and its distribution limited to the Red Sea are likely due to the isolation of that area during the Plio-Pleistocene sea-level drops related to glacioeustatic cycles. In this respect, several authors referred to these events in explaining the endemic distribution of a number of marine taxa in the Red Sea (see Lessios et al. 2001 and references therein). The close similarity of B. (A.) alfredensis to B. (A.) manilensis could reflect relationships of direct peripatric derivation, although the absence of data in the fossil record leaves the question open currently.

    The present-day pattern of distribution suggests two hypotheses for the origin of the American group. The first hypothesis supports its origin from the Indo-West Pacific group in the South African region and its subsequent northward Atlantic radiation. It is mainly based on the geographical sub-continuity of the present-day distribution among the two groups along the South African coasts. However, B. (A.) truncata, a species of the American group occurring today also along the southern coasts of western Africa, was already widespread in the Atlantic region during the Pleistocene. This would suggest an older origin for the American group. However, the fossil record testifies that the distribution of the Indo-West Pacific group in pre-Pleistocene times was located far from South Africa.

    The second hypothesis seems to be in accordance with the fossil record. It interprets the origin of the American group as from the ancient European stock, presumably during the Late Pliocene, by dispersal towards the eastern coasts of North America followed by a rapid southward diffusion. This hypothesis is supported also by the fact that the North Atlantic species of the ancient European stock have the umbo placed almost at one third of the shell length, which is a feature characterising the American group. B. (A.) dumortieri shows the subtruncate posterior margin as well (Fig. 6B).

    This consideration, and those discussed above on the origin of the Indo-West Pacific group, would indicate that the morphological differentiation distinguishing the American group from the Indo-West Pacific group arose early within the European—Paratethyan stock.

    The close affinities, underlined by Turner (1954), between B. (A.) truncata and B. (A.) subtruncata most probably reflect relationships of vicariance regulated by the last phases of emergence of the Panama Isthmus. As known (Duque-Caro 1990; Haug and Tiedemann 1998) that area was a stable sea connection until the Middle Pliocene and, before its full closure in the Late Pliocene it acted as a narrow and shallow seaway for the near-shore faunas (Nesis 2003). During the Early Pleistocene interglacial periods of sea-level rise, brief and intermittent shallow marine connections probably re-established (Beu 2001). The specialisation to mud and peat deposits (Turner 1954) and the relatively restricted geographical distribution of B. (A.) lamellosa would indicate its origin by speciation at the southern margin of the expansion of B. (A.) truncata.

    Fig. 9.

    Cladistic analysis of pholadoidean bivalve Barnea (Anchomasa) Leach, 1852 obtained by processing the matrix in Appendix 4. Exhaustive search with constraints enforcing the relationships among the outgroup taxa in order to reproduce the distribution of the supraspecific characters and the topology of the cladogram in Fig. 3. Strict consensus of three most parsimonious cladograms (L 21, CI 0.62, RI 0.74, RC 0.46). Unsupported nodes collapsed. See text for the definition of the cladistic parameters. Symbols as in Fig. 3.


    Phylogeny and historical biogeography

    A simple cladistic test of the relationships among the species of B. (Anchomasa), founded on the characters distinguishing the biogeographical groups described above, was performed in order to verify the hypotheses of historical biogeography. The type species of Talona, the genus that the phylogenetic analysis of the Pholadoidea indicates as retaining the highest number of plesiomorphies, and the respective type species of Pholas s.S., P. (Monothyra), C. (Scobinopholas) and Cyrtopleuropsis (Appendix 3), composing the sister-group of the Barnea clade, were selected as outgroup.

    The analysis was accomplished by forcing closest relationships among the outgroup species in order to reproduce the same topology as that of the cladogram shown in Fig. 3. Moreover, the supraspecific characters (characters 1–8 in Appendix 3) were polarised to ensure the same distribution of their state changes. Two species of Barnea s.s. were included, namely Barnea (Barnea) ustjurtensis Osipov, 1932, which is one of the earliest representative of the subgenus (early middle Miocene of Eastern Paratethys, Studencka et al. 1998), and the type species Barnea (Barnea) Candida (Linnaeus, 1758). B. (B.) ustjurtensis differs from B. (B.) Candida in the less strongly anterior umbo and in the slightly less strongly tapered shape of the shell. These aspects can be considered as components of the morphological variation of Barnea s.s., as is the case for B. (Anchomasa).

    The strict consensus tree (Fig. 9), although highly unresolved due to the very low number of characters involved, demonstrates the close relationships between the European species and the American group. In contrast, B. (A.) ujratamica and the species of the Indo-West Pacific group fall within a polytomic area of the cladogram. Indeed, in the context of the selected characters, the Indo-West Pacific group lacks synapomorphies differentiating it from the Paratethyan species. The comparison between the cladogram and the (palaeo)geographical distribution of the different species (Fig. 9) clearly illustrates the origin of the present-day biogeographical pattern. During the vicariant event related to the closure of the western Tethys, the Indo-West Pacific group and the Paratethyan species retained the same characters. In the present-day distribution, these characters appear to be exclusive of the Indo-West Pacific group but this is the effect of the disappearance of the Paratethyan species.

    The cladogram also clarifies the reasons for the polytomic structure of the Barnea clade. In the context of the selected characters, the broad pedal gape is the only feature distinguishing the Indo-West Pacific group and B. (A.) ujratamica from the Barnea s.s. species. This is a plesiomorphy of the Pholadinae which changes to a narrow, slit-like pedal gape in Barnea s.s. (Fig. 4).


    The cladistic analysis based on morphological data indicates that the Pholadoidea are a monophyletic group. The phylogenetic reconstruction, although consistent in some respect with Hoagland and Turner's (1981) cladogram (Fig. 5), suggests a taxonomic arrangement of Pholadoidea different from that proposed by Turner (1969). In detail, a classification of the Pholadoidea should mainly reflect the restricted composition of Pholadinae, the close relationships between Jouannetiinae and Martesiinae and between Xylophagainae and Teredinidae, and the paraphyletic condition of the Martesiinae. Moreover, it should also take into consideration that these groups are members of a major clade which is the sister-group of the Pholadinae clade. The analysis also demonstrated that Barnea s.s. and B. (Umitakea) are the closest relatives of B. (Anchomasa) and compose an unresolved clade within the Pholadinae.

    The morphological analysis and the study of the present-day distribution of the species of B. (Anchomasa) permitted to identify two biogeographical groups, namely the American and the Indo-West Pacific groups. The fossil record and the known geodynamic scenario suggest relationships of direct derivation between the Eastern Paratethyan species and the Indo-West Pacific group reflecting a vicariant event related to the Tethyan closure in middle Miocene times. The American group originated from the European stock by dispersion towards the western coasts of the northern Atlantic region, probably during the Late Pliocene.

    Insofar as the relationships between Barnea s.s. and B. (Anchomasa) are concerned, the oldest Barnea s.s. species are known from the Chokrakian to Konkian (early Langhian to early Serravallian in Studencka et al.'s 1998 time correlation chart; late Langhian to early Serravallian in Harzhauser and Piller's 2007 time correlation chart) of the Paratethyan region (Osipov 1932; Merklin and Nevesskaya 1955; Zhizhchenko 1959; Nevesskaya et al. 1993; Studencka et al. 1998), i.e., just slightly younger than B. (A.) ujratamica. This evidence and the results of the cladistic analysis suggest that Barnea s.s. originated from B. (Anchomasa) by the loss of a broad pedal gape, and that the divergence probably began during the early middle Miocene. The presence of at least four species in the middle Miocene of Eastern Paratethys (Studencka et al. 1998) would testify that Barnea s.s. underwent a strong and rapid differentiation in that area after its appearance.

    Finally, the fossil record and the present-day biogeographical distribution would indicate as plausible the origin of B. (Umitakea) from B. (Anchomasa) in the western Pacific area. In fact, B. (Umitakea) is known from the Pliocene deposits of Indonesia, Taiwan, and Japan (Yokoyama 1920; Evseev 1993; Robba et al. 2002). Today, it is widespread in the western Pacific area, from the Bay of Bengal to Australia and, eastwards, to Japan (Higo et al. 1999; Robba et al. 2002). As mentioned above, B. (Taiwanobarnea), a taxon known from the late Miocene of Taiwan (Wang, 1983), although lacking information on the internal shell characters, shows the closest similarities with B. (Umitakea) but also features transitional to B. (Anchomasa). As a matter of speculation, this could suggest that such a derivation arose early, just after the beginning of the dispersion of B. (Anchomasa) into the Indo-Pacific region.


    I am grateful to Umberto Nicosia (Department of Earth Sciences, University “La Sapienza”, Rome, Italy) for the numerous, pleasant and helpful discussions on the application of the cladistic method in palaeontology. I am indebted to Jack A. Grant-Mackie (Department of Geology, University of Auckland, New Zealand) and Alan G. Beu (Paleontology and Environmental Change Section, GNS Science, Lower Hutt, New Zealand) for complementary data concerning the fossil record and Neogene stratigraphy of New Zealand. Simon R. A. Kelly (CASP, University of Cambridge, United Kingdom), Alan G. Beu and an anonymous referee are gratefully acknowledged for their critical reading and suggestions leading to the improvement of an earlier version of the manuscript. The photographic work and technical drawings were executed by Stefano Castelli and Nicola Michelon (Department of Geo-sciences, University of Padua, Italy), respectively. The paper was supported by funds 60A05-5953/07 and CPDA072218/07 of the University of Padua.


    1. R.T. Abbott 1954. American Seashells. 141 pp. Van Nostrand, Princeton, New Jersey. Google Scholar

    2. J. Allan 1950. Australian Shells: with Related Animals Living in the Sea, in Freshwater and on the Land. 470 pp. Georgian House, Melbourne. Google Scholar

    3. M.R.W. Amler 1999. Synoptical classification of fossil and Recent Bivalvia. Geologica et Palaeontologica 33: 237–248. Google Scholar

    4. L.C. Anderson and P.D. Roopnarine 2003. Evolution and phylogenetic relationships of Neogene Corbulidae (Bivalvia; Myoidea) of Tropical America. Journal of Paleontology 77: 1086–1102. Google Scholar

    5. A.D. Ansell and N.B. Nair 1969. The mechanisms of boring in Martesia striata Linné (Bivalvia: Pholadidae) and Xylophaga dorsalis Turton (Bivalvia: Xylophaginidae). Proceedings of the Royal Society of London. Series B, Biological Sciences 174: 123–133. Google Scholar

    6. S.M. Baker and D.K. Padilla 2004. New frontiers in functional morphology of molluscs: a tribute to Drs. Vera Fretter and Ruth Turner. American Malacological Bulletin 18: 121–127. Google Scholar

    7. P. Bartsch 1915. Report on the Turton collection of South African marine mollusks, with additional notes on other South African shells contained in the United States national museums. United States National Museum Bulletin 91: 1–305. Google Scholar

    8. F.R. Bernard , Y.-Y. Cai , and B. Morton 1993. Catalogue of the Living Marine Bivalve Molluscs. 146 pp. Hong Kong University Press, Hong Kong. Google Scholar

    9. A.G. Beu 2001. Gradual Miocene to Pleistocene uplift of the central American Isthmus: evidence from tropical American tonnoidean gastropods. Journal of Paleontology 75: 706–720. Google Scholar

    10. A.G. Beu 2006. Marine Mollusca of Oxygen Isotope Stages of the last 2 million years in New Zealand. Part 2. Biostratigraphically useful and new Pliocene to Recent bivalves. Journal of the Royal Society of New Zealand, 36: 151–338. Google Scholar

    11. A.G. Beu and P.A. Maxwell 1990. Cenozoic Mollusca of New Zealand. New Zealand Geological Survey Paleontological Bulletin 58: 1–518. Google Scholar

    12. D.T. Bosch , S.P. Dance , R.G. Molenbeek , and P.G. Oliver 1995. Seashells of Eastern Arabia. 296 pp. S. Peter Dance, Motivate Publishing, Dubai. Google Scholar

    13. A. Carcelles 1944. Catalogo de los molluscos marinos de Puerto Quequén (República Argentina). Revista del Museo de La Plata, Nueva Serie 3, Zoologia 23: 233–309. Google Scholar

    14. L. Castagnolo , Franchini D. , and F. Giusti 1980. Vol. 10: Bivalvi (Bivalvia). In : F. Ruffo (ed.), Guide al riconoscimento delle specie animali delle acque interne italiane, 64 pp. Consiglio Nazionale delle Ricerche, Roma. Google Scholar

    15. C. Chaix and B. Cahuzac 2005. Les faunes de Scléractiniaires dans les faluns du Miocène moyen d'Atlantique-Est (bassins de la Loire et d'Aquitaine): paléobiogéographie et évolution climatique. Annales de Paléontologie 91: 33–72. Google Scholar

    16. P.E. Chanley 1965. Larval development of a boring clam, Barnea truncata. Chesapeake Science 6: 162–166. Google Scholar

    17. W.J. Clench and R.D. Turner 1946. The genus Bankia in the western Atlantic. Johnsonia 2: 1–28. Google Scholar

    18. W.H. Dall 1898. Contributions to the Tertiary fauna of Florida, with special references to the Miocene silex-beds of Tampa and the Pliocene beds of the Caloosahatchie river including in many cases a complete revision of generic groups treated of and their American Tertiary species. Part IV. I, Prionodesmacea: Nucula to Julia. II, Peleodesmacea: Teredo to Ervilia. Transactions of the Wagner Free Institute of Science of Philadelphia 3: 571–947. Google Scholar

    19. G.P. Deshayes 1874. Description de quelques espèces de mollusques nouveaux ou peu connus envoyés de la Chine par l'Abbé A. David. Nouvelles Archives du Muséum d'Histoire Naturelle de Paris 9: 1–14. Google Scholar

    20. P. Doderlein 1862. Cenni geologici intorno la giacitura dei terreni miocenici dell'Italia centrale. Atti del X Congresso degli Scienziati Italiani tenuto a Siena nel Settembre 1862: 1–25. Google Scholar

    21. G.F. Dolfuss and P. Dautzenberg 1902. Conchyliologie du Miocène moyen du Basin de la Loire. Première Partie: Pélécypodes. Mémoires de la Société Géologique de France, Paléontologie 10, Mémoire 27: 1–106. Google Scholar

    22. F. Dujardin 1837. Mémoire sur les couches du Sol en Touraine. Mémoires de la Société Géologique de France 2, Mémoire 9: 211–311. Google Scholar

    23. H. Duque-Caro 1990. Neogene stratigraphy, paleoceanography and paleobiogeography in northwest South America and the evolution of the Panama seaway. Palaeogeography, Palaeoclimatology, Palaeoecology 77: 203–234. Google Scholar

    24. G.A. Evseev 1993. Anatomy of Barnea japonica (Bivalvia, Pholadidae). Ruthenica 3: 31–49. Google Scholar

    25. P. Fischer 1866. Description de nouvelles espèces d'invertébrés fossiles dans le bassin du Rhône (formation tertiaire moyen). In : A. Faisan and A. Locard (eds.), Monographie géologique du Mont d'Or Lyonnais et de ses dépendances, 434–440. Savy, Paris, Lyon. Google Scholar

    26. J.E. Fitch 1953. Common bivalves of California. Fish Bulletin of the Department of Fish and Game of California, Marine Fisheries Branch 90: 1–106. Google Scholar

    27. F. Franco 1982. Molluschi indomediterranei tardopaleogenici e neogenici. Bollettino della Società Paleontologica Italiana 21: 277–282. Google Scholar

    28. G. Giribet and D. Distel 2003. Bivalve phylogeny and molecular data. In : C. Lydeard and D.R. Lindberg (eds.), Molecular Systematics and Phylogeography of Mollusks, 45–90. Smithsonian, Washington. Google Scholar

    29. G. Giribet and W. Wheeler 2002. On bivalve phylogeny: a high-level analysis of the Bivalvia (Mollusca) based on combined morphology and DNA sequence data. Invertebrate Biology 121: 271–324. Google Scholar

    30. M. Gilbert 1963. Révision de la faune d'invertébrés du Diestien typique. Mémoires de la Société belge de Géologie 6: 40–45. Google Scholar

    31. M. Gilbert and L. Van De Poel 1966. Les Bivalvia fossiles du Cénozoïque étranger des collections de l'Institut Royal des Sciences Naturelles de Belgique. III. Heteroconchia. 1re partie: Laternulidae à Chamidae. Mémoires de l'nstitut Royal des Sciences Naturelles de Belgique, 2me série 81: 1–82. Google Scholar

    32. D.R. Gregg 1960. The geology of Tongariro Subdivision. New Zealand Geological Survey Bulletin 40: 1–152. Google Scholar

    33. T. Haga and T. Kase 2007. Molecular phylogeny and morphological evolution of pholadoidean boring bivalves (Bivalvia: Myoida). In : K. Jordaens , N. Van Houtte , J. Van Goethem , and T. Backeljau (eds.), World Congress of Malacology Antwerp, Belgium, 15–20 July 2007, Abstracts, 89. Unitas Malacologica, Antwerp. Google Scholar

    34. M. Harzhauser and W.E. Piller 2007. Benchmark data of a changing sea. Palaeogeography, palaeobiogeography and events in the Central Paratethys during the Miocene. Palaeogeography, Palaeoclimatology, Palaeoecology 253: 8–31. Google Scholar

    35. G.H. Haug and R. Tiedemann 1998. Effect of the formation of the Isthmus of Panama on Atlantic Ocean thermohaline circulation. Nature 393: 673–676. Google Scholar

    36. S. Hayasaka 1969. Molluscan fauna of the Kukinaga Group in Tané-gashima, south Kyűshű, Japan. Reports of the Faculty of Sciences, Kagoshima Unversity (Earth Science, Biology) 2: 33–52. Google Scholar

    37. C. Hedley 1893. Pholas obturamentum, an undescribed bivalve from Sydney Harbour. Records of the Australian Museum 2: 55–57. Google Scholar

    38. S. Higo , P. Callomon , and Y. Gotô 1999. Catalogue and Bibliography of the Marine Shell-bearing Mollusca of Japan. Gastropoda, Bivalvia, Polyplacophora, Scaphopoda. 749 pp. Elle Scientific Pubblications, Osaka. Google Scholar

    39. K.E. Hoagland 1983. Characters, character states, and taxa used in multivariate analysis of the Pholadacea. Tryonia 8: 1–51. Google Scholar

    40. K.E. Hoagland and R.D. Turner 1981. Evolution and adaptive radiation of wood-boring bivalves (Pholadacea). Malacologia 21: 111–148. Google Scholar

    41. K. Inoue 2007. Batillariid and potamidid gastropods from the Middle Miocene Kukinaga Group, Tanegashima Island, southwest Japan, and their paleobiogeographic implications. Paleontological Research 11: 277–292. Google Scholar

    42. Y. Ito 1998. Hinge development and functional morphology in the larvae and early postlarvae of the boring bivalve, Barnea manilensis (Pholadidae). Venus 57: 191–207. Google Scholar

    43. Y. Ito 1999. Ontogenetic changes in boring behaviour by the rock-boring bivalve, Barnea manilensis (Pholadidae). The Veliger 42: 157–168. Google Scholar

    44. A.W. Janssen , G.A. Peeters , and L. Van Der Slik 1984. De fossiele schelpen van de Nederlandse stranden en zeegaten, tweede serie, 8 (slot). Basteria 48: 91–219. Google Scholar

    45. A.M. Keen 1958. Sea Shells of Tropical West America. Marine Mollusks from Lower California to Colombia. 624 pp. Stanford University Press, Stanford, California. Google Scholar

    46. A.M. Keen 1969. Superfamily Myacea Lamarck, 1809. In : R.C. Moore and C. Teichert (eds.), Treatise on Invertebrate Paleontology. Part N, Mollusca 6, Bivalvia 2 (3), N690–N699. Geological Society of America and University of Kansas Press, Boulder, Colorado. Google Scholar

    47. A.M. Keen and R. Dance 1969. Family Pisidiidae Gray, 1857. In : R.C. Moore and C. Teichert (eds.), Treatise on Invertebrate Paleontology. Part N, Mollusca 6, Bivalvia 2(3), N669–N670. Geological Society of America and University of Kansas Press, Boulder, Colorado. Google Scholar

    48. S.R.A. Kelly 1988a. Cretaceous wood-boring bivalves from western Antarctica with a review of the Mesozoic Pholadidae. Palaeontology 31: 341–372. Google Scholar

    49. S.R.A. Kelly 1988b. Turnus? davidsoni (de Loriol), the earliest British pholadid wood-boring bivalve, from the Late Jurassic of Oxfordshire. Proceedings of the Geological Association 99: 43–47. Google Scholar

    50. G.L. Kennedy 1974. West American Cenozoic Pholadidae (Mollusca: Bivalvia). San Diego Society of Natural History, Memoir 8: 1–128. Google Scholar

    51. G.L. Kennedy 1993. New Cretaceous and Tertiary Pholadidae (Mollusca: Bivalvia) from California. Journal of Paleontology 67: 397–404. Google Scholar

    52. G.L. Kennedy and J.M. Armentrout 1989. A new species of chimney-building Penitella from the Gulf of Alaska, Bivalvia: Pholadidae. The Veliger 32: 320–325. Google Scholar

    53. B. Kensley and J. Pether 1986. Late Tertiary and Early Quaternary fossil Mollusca of the Hondeklip area, Cape Province. South Africa. Annals of the South African Museum 97: 141–225. Google Scholar

    54. I.W. Keyes 1972. Biological type specimens in the New Zealand Geological Survey. II. Cenozoic bivalve and scaphopod Mollusca. New Zealand Geological Survey Paleontological Bulletin 45: 1–113. Google Scholar

    55. Y. Kikuchi , A. Nikaido , and M. Sugaya 1991. Hard substratum boring shells from the Pliocene Kume Formation in Ibaraki Prefecture, northern Kanto, Japan. University of Tsukuba Institute of Geoscience, Annual Report 17: 48–51. Google Scholar

    56. K. Kodama , T. Ozawa , K. Inoue , Y. Maeda , and T. Takeuchi 1991. Paleomagnetism and post-Middle Miocene counter-clockwise rotation of Tanegashima Island off Kyushu, Japan. Journal of Geomagnetism and Geoelectricity 43: 721–740. Google Scholar

    57. A.V. Korniushin and M. Glaubrecht 2002. Phylogenetic analysis based on the morphology of viviparous freshwater clams of the family Sphaeriidae (Mollusca, Bivalvia, Veneroida). The Norwegian Academy of Science and Letters, Zoologica Scripta 31: 415–459. Google Scholar

    58. K. Khin and Myitta 1999. Marine transgression and regression in Miocene sequences of northern Pegu (Bago) Yoma, Central Myanmar. Journal of Asian Earth Sciences 17: 369–393. Google Scholar

    59. K. Lamprell and J. Healy 1998. Bivalves of Australia. Volume 2. 288 pp. Backhuys Publishers, Leiden. Google Scholar

    60. T. Lee 2001. Systematic revision of the Sphaeriinae (Mollusca, Bivalvia, Veneroida, Sphaeriidae). 210 pp. Unpublished PhD dissertation, University of Michigan. Available at  http://www.ummz.umich.eduGoogle Scholar

    61. H.A. Lessios , B.D. Kessing , and J.S. Pearse 2001. Population structure and speciation in tropical seas: global phylogeography of the sea urchin Diadema. Evolution 55: 955–975. Google Scholar

    62. A. Locard 1878. Description de la faune de la mollasse marine et d'eau douce du Lyonnais et du Dauphiné. Archives du Museum d'Histoire Naturelle de Lyon 2: 1–279. Google Scholar

    63. S.G.B.C. Lopes , O. Domaneschi , D.T. De Morales , M. Morita , and G. de L.C. Meserani 2000. Functional anatomy of the digestive system of Neoteredo reynei (Bartsch, 1920) and Psiloteredo healdi (Bartsch, 1931) (Bivalvia: Teredinidae). In : E.M. Harper , J.D. Taylor , and J.A. Crame (eds.), The evolutionary biology of the Bivalvia. Geological Society of London, Special Publication 177: 257–271. Google Scholar

    64. J. Marwick 1931. The Tertiary Mollusca of the Gisborne District. New Zealand Geological Survey Palaeontological Bulletin 13: 1–177. Google Scholar

    65. R.L. Merklin and L.A. Nevesskaya [Nevesskaâ , L.A.] 1955. Classification key for the determination of the Miocene mollusc bivalves of Turkmenia and western Kazakhstan [in Russian]. Trudy Paleontologičeskogo Instituta, Rossijskaâ Akademiâ Nauk SSSR 58: 1–116. Google Scholar

    66. S. Monari ( 2008). Barnea (Anchomasa) parva (Pennant, 1777) (Pholadidae, Bivalvia) in the Pleistocene sediments of northern Latium (central Italy). Bollettino della Societá Paleontologica Italiana 47: 203–210. Google Scholar

    67. K.N. Nesis 2003. Distribution of recent Cephalopoda and implications for Plio-Pleistocene events. Berliner Paläobiologische Abhandlungen 3: 199–224. Google Scholar

    68. L.A. Nevesskaya [Nevesskaâ, L.A.] , I.A. Goncharova [Gončarova, I.A.], N.P . Paramonova, S.V. Popov , E.V. Babak , K.G. Bagdasaryan [Bagdasarân, K.G.] and A.A. Voronina 1993. A key to the Miocene bivalve molluscs of south western Eurasia [in Russian]. Trudy Paleontologičeskogo Instituta, Rossijskaâ Akademiâ Nauk SSSR 247: 1–412. Google Scholar

    69. M. Nicklès 1950. Mollusques testacés marins de la côte occidentale d'Afrique. 269 pp. Lechevalier, Paris. Google Scholar

    70. M. Nicklès 1955. Schaphopodes et lamellibranches récoltés dans l'Ouest Africain. In : A. Bruun (ed.), Atlantide-Report n° 3. Scientific Results of the Danish Expedintion to the Coasts of Tropical West Africa 19451946, 93–237. Danish Science Press, Copenhagen. Google Scholar

    71. F. Noetling 1901. The fauna of the Miocene beds of Burma. Part 3. Memoirs of the Geological Survey of India, Palaeontologia Indica, New Series, 1: 1–378. Google Scholar

    72. P.H. Nyst 1843. Description des coquilles et des polypiers fossiles des terrains tertiaries de la Belgique. 675 pp. Hayez, Académie Royale de Belgique, Bruxelles. Google Scholar

    73. P.H. Nyst 1878–81. Conchyliologie des terrains tertiaires de la Belgique. Première Partie. Terrain Pliocène Scaldisien. Annales Musée Royal d'Histoire Naturelle de Belgique 3: 1–263. Google Scholar

    74. M. Okamoto and T. Habe 1987. Description of Nipponopholas satoi n. gen. & n. sp. Venus 46: 133–136. Google Scholar

    75. P.G. Oliver 1992. Bivalved Seashells of the Red Sea. 330 pp. Verlage Christa Hemmen, Wiesbaden. Google Scholar

    76. A. Orbigny (d') 1835–1847. Voyage dans l'Amerique Méridionale (le Brésil, la République orientale de l'Uruguay, la République Argentine, la Patagonie, la République du Chili, la République de Bolivia, la République du Pérou) pendant les années 1826, 1827, 1828, 1829, 1830, 1831, 1832 et 1833. Tome cinquième. 3eme Partie: Mollusques. 758 pp. Bertrand, Paris. Google Scholar

    77. S.S. Osipov 1932. Karaganian and Konkian horizons [in Russian]. In : A.D. Arhangelskij and L.Š. Davitašvili (eds.), Rukovodâŝie iskocaemye neftenosnyh rajonov Krymsko-Kavkazskoi oblasti. Trudy Gosudarstvennogo Issledovatel'skogo Neftânogo Instituta 3/4: 1–82. Google Scholar

    78. J.M. Pacaud 1998. Un nouveau genre de Pholadidae (Mollusca, Bivalvia) du Paléogène inférieur du nord de l'Atlantique. Apex 13: 63–75. Google Scholar

    79. P. Pallary 1900. Coquilles marines du littoral du département d'Oran. Journal de Conchyliologie 48: 211–422. Google Scholar

    80. T. Pennant 1777. British Zoology. Volume IV. Crustacea, Mollusca, Testacea. 156 pp. Warrington, London. Google Scholar

    81. D.A.B. Phillips , C.P. Handreck , P.E. Bock , R. Burn , B.J. Smith , and D. A. Staples 1984. Coastal Invertebrates of Victoria. An Atlas of Selected Species. 168 pp. Marine Research Group of Victoria and Museum of Victoria, Melbourne. Google Scholar

    82. G. Piccoli 2002. Tethyan exchange of benthic molluscs between SE Asia and Mediterranean in the Paleogene. Memorie di Scienze Geologiche 54: 1–8. Google Scholar

    83. G. Piccoli , S. Sartori , A. Franchino , R. Pedron , L. Claudio , and A.R. Natale 1991. Mathematical model of faunal spreading in the benthic palaeobiogeography (applied to Cenozoic Tethyan molluscs). Palaeogeography, Palaeoclimatology, Palaeoecology 86: 139–196. Google Scholar

    84. J.M. Poutiers 1998. Bivalves. In : K.E. Carpenter and V.H. Niem (eds.), FAO species identification guide for fishery purposes. The living marine resourches of the western central Pacific. Vol. 1: seaweeds, corals, bivalves and gastropods, 123–362. FAO, Rome. Google Scholar

    85. R.J. Pumphrey 1938. The double innervation of muscles in the clam (Mya arenaria). Journal of Experimental Biology 15: 500–505. Google Scholar

    86. R.D. Purchon 1941. On the biology and relationship of the lamellibranch Xylophaga dorsalis (Turton). Journal of the Marine Biological Association of the United Kingdom 25: 1–39. Google Scholar

    87. R.D. Purchon 1955. The structure and function of the British Pholadidae (rock-boring Lamellibranchia). Proceedings of the Zoological Society of London 124: 859–911. Google Scholar

    88. R.D. Purchon 1987. The stomach of the Bivalvia. Philosophical Transactions of the Royal Society of London, Series B, Biological Sciences 316: 183–276. Google Scholar

    89. E. Robba 1987. The final occlusion of Tethys: its bearing on Mediterranean benthic molluscs. Proceedings of the International Symposium on Shallow Tethys 2: 405–426. Google Scholar

    90. E. Robba , I. Di Geronimo , N. Chaimanee , M.P. Negri , and R. Sanfilippo 2002. Holocene and Recent shallow soft-bottom mollusks from the northern Gulf of Thailand area: Bivalvia. Bollettino Malacologico 38: 9–132. Google Scholar

    91. H. Röder 1977. Zur Beziehung zwischen Konstruktion und Substrat bei mechanisch bohrenden Bohrmuscheln (Pholadidae, Teredinidae). Senckenbergiana Maritima 9: 105–213. Google Scholar

    92. F. Rögl 1998. Paleogeographic considerations for Mediterranean and Paratethys seaways (Oligocene to Miocene). Annalen der Naturhistorisches Museum Wien 99A: 279–310. Google Scholar

    93. F. Rögl 1999. Mediterranean and Paratethys. Facts and hypotheses of an Oligocene to Miocene paleogeography (short review). Geologica Carpatica 50: 339–349. Google Scholar

    94. F. Sacco 1901. I molluschi dei terreni terziarii del Piemonte e della Liguria. Parte 29 (Donacidae—Clavagellidae). 161 pp. Clausen, Torino. Google Scholar

    95. Z.V. Sakhelashvili [Sahelašvili, Z.V.] 1965. The fauna from the oyster layers in Gori [in Russian]. Trudy Geologičeskogo Instituta, Akademiâ Nauk Gruzinskoj SSR, Geologičeskaâ seriâ 14: 129–174. Google Scholar

    96. E. Savazzi 1982. Adaptations to tube dwelling in Bivalvia. Lethaia 15: 275–297. Google Scholar

    97. T. Say 1922. An account of some of the marine shells of the United States (continued from page 276). Journal of the Academy of Natural Sciences of Philadelphia 2: 302–325. Google Scholar

    98. F. Scarabino 2003. Lista sistemática de los Bivalvia marinos y estuarinos viventes de Uruguay. Comunicaciones de la Sociedad Malacológica del Uruguay 8: 229–259. Google Scholar

    99. W. Sissingh 1998. Comparative Tertiary stratigraphy of the Rhine Graben, Bresse Graben and Molasse Basin: correlation of Alpine foreland events. Tectonophysics 300: 249–284. Google Scholar

    100. A.B. Smith 1994. Systematics and the Fossil Record. Documenting Evolutionary Patterns. 113 pp. Blackwell Science, Oxford. Google Scholar

    101. E.D. Smith 1969. Functional morphology of Penitella conradi relative to shell-penetration. American Zoologist 9: 869–880. Google Scholar

    102. J. Sowerby 1818. The Mineral Conchology of Great Britain; or Coloured Figures and Description of Those Remains of Testaceous Animals or Shell, which Have Been Preserved at Various Times and Depths in the Earth. Volume II. 251 pp. Arding and Merrett, London. Google Scholar

    103. G.R. Stevens 1994. Developing trends in south western Pacific biogeography in Late Mesozoic and Cenozoic times. In : G. Pallini (ed.), Proceedings of the 3rd Pergola International Symposium “Fossili, Evoluzione, Ambiente”, Pergola 25–30 October 1990. Palaeopelagos Special Pubblication 1, Appendix: 397–420. Google Scholar

    104. B. Studencka , I.A. Gontsharova , and S.V. Popov 1998. The bivalve fauna as a basis for reconstruction of the middle Miocene history of the Paratethys. Acta Geologica Polonica 48: 285–342. Google Scholar

    105. H. Suter 1913. Manual of the New Zealand Mollusca. 1120 pp. J. MacKay, Government Printer, Wellington. Google Scholar

    106. H. Suter 1921. Lists of New Zealand Tertiary Mollusca from various localities examined and named from 1913 to the end of 1917 (a few emended lists, previously published elsewhere, are added) with notes and a review of results, etc. by P.G. Morgan. New Zealand Geological Survey Palaeontological Bulletin 8: 1–107. Google Scholar

    107. D.L. Swofford 1998. PAUP*. Phylogenetic Analysis Using Parsimony (*and other methods). Version 4. Sinauer Associated, Sunderland, Massachussetts. Google Scholar

    108. J.D. Taylor , S.T. Williams , E.A. Glover , and P. Dyal 2007. A molecular phylogeny of heterodont bivalves (Mollusca: Bivalvia: Heterodonta): new analyses of 18S and 28S rRNA genes. Zoologica Scripta 36: 587–606. Google Scholar

    109. R.D. Turner 1954. The family Pholadidae in the Western Atlantic and the Eastern Pacific. Part 1: Pholadinae. Johnsonia 3: 1–64. Google Scholar

    110. R.D. Turner 1955. The family Pholadidae in the Western Atlantic and the Eastern Pacific, Part 2: Martesiinae, Jouannetiinae and Xylophaginae. Johnsonia 3: 65–100. Google Scholar

    111. R.D. Turner 1961. The genus Lignopholas Turner (Mollusca: Pholadidae). Mitteilungen aus dem Zoologischen Museum in Berlin 37: 287–295. Google Scholar

    112. R.D. Turner 1962. Nettastomella japonica Yokoyama in North America and notes on the Pholadidae. Occasional Papers on Mollusks 2: 289–308. Google Scholar

    113. R.D. Turner 1966. A Survey and Illustrated Catalogue of the Teredinidae (Mollusca : Bivalvia). 266 pp. Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts. Google Scholar

    114. R.D. Turner 1969. Superfamily Pholadacea Lamarck, 1809. In : R.C. Moore and C. Teichert (eds.), Treatise on invertebrate paleontology. Part N, Mollusca 6, Bivalvia 2(3), N702–N741. Geological Society of America and University of Kansas Press, Boulder, Colorado. Google Scholar

    115. R.D. Turner 1972a. A new genus and species of deep water wood-boring bivalve (Mollusca, Pholadidae, Xylophagainae). Basteria 36: 97–104. Google Scholar

    116. R.D. Turner 1972b. Xyloteredo, a new teredinid-like abyssal wood-borer (Mollusca, Pholadidae, Xylophagainae). Breviora 397: 1–19. Google Scholar

    117. R.D. Turner 1998. Superfamily Pholadoidea. In : P.L. Beesley , G.J.B. Ross , and A. Wells (eds.), Mollusca: The Southern Synthesis. Fauna of Australia. Volume 5, Part A, 371–396. CSIRO Publishing, Melbourne. Google Scholar

    118. R.D. Turner 2002. On the subfamily Xylophagainae (family Pholadidae, Bivalvia, Mollusca). [Final completion and revision by H. Ferranti]. Bulletin of the Museum of Comparative Zoology 157: 223–307. Google Scholar

    119. R.D. Turner and J.L. McKoy 1979. Bankia neztalia n.sp. (Mollusca: Bivalvia: Teredinidae) from Australia and New Zealand, and its relationships. Journal of the Royal Society of New Zealand 9: 465–473. Google Scholar

    120. R.D. Turner and L.N. Santhakumaran 1989. The genera Martesia and Lignopholas in the Indo-Pacific (Mollusca: Bivalvia: Pholadidae). Ophelia 30: 155–186. Google Scholar

    121. H.E. Vokes 1980. Genera of the Bivalvia: a Systematic and Bibliographic Catalogue (Revised and Updated). 307 pp. Paleontological Research Institution, Ithaca. Google Scholar

    122. B. Vrielynck , G.S. Odin , and J. Dercourt 1997. Miocene palaeogeography of the Tethys Ocean; potential global correlations in the Mediterranean. In : A. Montanari , G.S. Odin , and R. Coccioni (eds.), Miocene Stratigraphy: An Integrated Approach, 157–165. Elsevier Science, Amsterdam. Google Scholar

    123. C.J. Wandrey 2006. Eocene to Miocene composite total petroleum system, Irrawaddy-Andaman and north Burma geologic province, Myanmar, Chapter E. In : C.J. Wandrey (ed.), Petroleum systems and related geologic studies in Region 8, South Asia. U.S. Geological Survey Bulletin 2208-E: 1–26. Google Scholar

    124. C.C. Wang 1983. On a new subgenus and new species of pholadid bivalves from the Miocene of Taiwan. Bulletin of Central Geological Survey (Taipei) 2: 121–129. Google Scholar

    125. S.T. Williams and D.G. Reid 2004. Speciation and diversity on tropical rocky shores: a global phylogeny of snails of the genus Echinolittorina. Evolution 58: 2227–2251. Google Scholar

    126. E. Wilson and G.L. Kennedy 1984. The boring clam Penitella conradi (Bivalvia: Pholadidae) in nephrite from Monterey County, California. The Nautilus 98: 159–162. Google Scholar

    127. S.V. Wood 1850. A monograph of the Crag Mollusca or, descriptions of shells from the middle and upper Tertiaries of the east of England. Part 2. Bivalves. Palaeontographical Society Monograph 9: 217–342. Google Scholar

    128. S.V. Wood 1874. Supplement to the Monograph of the Crag Mollusca, with descriptions of shells from the upper Tertiaries of the east of England. Vol. 3. Univalves and Bivalves with an introductory outline of the geology of the same district, and map by S.V. Wood and F.W. Harmer. Palaeontographical Society Monograph 27: 99–231. Google Scholar

    129. M. Yokoyama 1920. Fossils from the Miura Pensinsula and its immediate north. Journal of the College of Sciences, Imperial University of Tokyo 39: 1–193. Google Scholar

    130. C.M. Yonge 1923. Studies on the comparative physiology of digestion. 1. The mechanism of feeding, digestion and assimilation in the lamellibranch Mya. Journal of Experimental Biology 1: 15–64. Google Scholar

    131. B.P. Zhizhchenko [Žižčenko, B.P.] 1959. Atlas of the Middle Miocene fauna of the northern Caucasus and Crimea [in Russian with English abstract]. Trudy Vsesoûznogo Naučno-Issledovatel'skogo Instituta Prirodnyh Gazov (VNIIGAZ): 1–386. Google Scholar


    Appendix 1

    List of characters and character states employed in the phylogenetic analysis of Pholadoidea.


    • 1. Size of the shell with respect to the soft body: not reduced (covering at least visceral mass) (0); reduced (covering only the anterior part of visceral mass) (1).

    • 2. Shape of adult valve (length/height ratio): sub-oval, globose (length slightly exceeding to almost equal height) (0); transversally elongated in antero-posterior direction (length clearly exceeding height) (1).

    • 3. Position of umbo: subcentral (0); moderately anterior (1); clearly anterior (2).

    • 4. Posterior slope: not lobed (0); lobed (1).

    • 5. Umbonal reflection: absent (0); present (1).

    • 6. Structure of umbonal reflection: simple (0); with transverse partitions (septate) (1).

    • 7. Funnel-shaped pit below the umbonal reflection: absent (0); present (1).

    • 8. Posterior part of umbonal reflection: adherent to the umbonal region (0); raised and with posterior margin square cut (1).

    • 9. Hinge teeth: present (0); absent (1).

    • 10. Ornament of anterior slope: absent (0); imbrications (1); fine denticulations (2).

    • 11. Periostracal leaves on the posterior slope: absent (0); present (1).

    • 12. Pedal gape: absent (0); present (1).

    • 13. Shape of pedal gape: slit-like (prora not differentiated) (0); broadly lanceolate (prora differentiated) (1); angulated embayment (prora small and auricle-like) (2).

    • 14. Chondrophore on left valve of adult shell: absent (0); present (1).

    • 15. Apophyses: absent (0); present (1).

    • 16. Shape of apophysis: long, narrow (0); large, spatulate to spoon-shaped (1).

    • 17. Umbonal-ventral ridge on the internal surface of the adult valve (corresponding to the external umbonal-ventral sulcus): absent (0); present (1).

    • 18. Dorsal condyle in adult shell: absent to weak (modified umbo) (0); well developed (1).

    • 19. Ventral condyle in adult shell: absent (0); weak (1); prominent (2).

    • 20. Radial sulcus dividing the disc from the posterior slope: absent (0); present (1).

    Accessory structures of the shell

    • 21. Callum: absent (0); present (1). The callum develops in taxa having pedal gape. Taxa without pedal gape (character 12 state 0) have that character codified as not applicable (N).

    • 22. Development of callum: symmetrical (0); left part more extended and overlapping right part (1).

    • 23. Dorsal extension of the callum: absent (0); present (1).

    • 24. Protoplax: absent (0); present (1).

    • 25. Composition of the protoplax: chitinous (0); calcareous (1).

    • 26. Structure of the protoplax: single piece (0); subdivided in two pieces (1).

    • 27. Mesoplax: absent (0); present (1).

    • 28. Structure of the mesoplax: single piece (0); subdivided in two pieces (1).

    • 29. Posterior area of umbonal reflection modified for reception of mesoplax: no (0); yes (1).

    • 30. Metaplax: absent (0); present (1).

    • 31. Hypoplax: absent (0); present (1).

    • 32. Siphonoplax: absent (0); present (1).

    • 33. Development of siphonoplax: on both valves (0); on right valve only (1).

    • 34. Tube lining burrow: absent (0); present (1).

    • 35. Pallets: absent (0); present (1).

    • 36. Structure of pallets: not segmented (0); segmented (1).

    Soft parts

    • 37. Adult foot: not atrophied (0); atrophied (1).

    • 38. Shape of foot: tongue-shaped or hatchet-shaped (0); cylindrical with discoid extremity (1).

    • 39. Gills: two demibranchs (0); single demibranch (1).

    • 40. Position of gills: before posterior adductor muscle (0); beyond posterior adductor muscle (1).

    • 41. Shape of ctenidia: short and wide (0); elongate (1).

    • 42. Loop of visceral mass beyond the posterior adductor muscle: absent (adductor muscles far apart) (0); present (adductor muscles close together) (1).

    • 43. Intestine: transversing heart (0); not transversing heart (1).

    • 44. Position of visceral ganglion: near the ventral side of posterior adductor muscle (0); posterior, at the end of pericardium (1).

    • 45. Wood-storing caecum: absent (0); present (1).

    • 46. Labial palps: large, free at the tips (0); small, not free at the tips (1).

    • 47. Insertions of siphonal retractors: on shell valves (0); on burrow lining (1); on siphonal plates (2).

    Appendix 2

    Data matrix showing the distribution of the character states of 47 characters in 39 taxa included in the phylogenetic analysis of the Pholadoidea.


    Appendix 3

    Characters and character states employed for a basal phylogenetic analysis of the subgenus Barnea (Anchomasa).

    1. Umbonal reflection: simple (0); septate (1). (character 5 in Appendix 1)

    2. Posterior part of umbonal reflection: raised and with posterior margin square cut (0); adherent to the umbonal region (1). (character 8 in Appendix 1)

    3. Pedal gape: absent (0); present (1). (character 12 in Appendix 1)

    4. Shape of pedal gape: broad (0); slit-like (1). (character 13 in Appendix 1)

    5. Shape of apophyses: thin (0); spatulate (1). (character 16 in Appendix 1)

    6. Protoplax: absent (0); present (1). (character 24 in Appendix 1)

    7. Mesoplax: absent (0); present (1). (character 27 in Appendix 1)

    8. Metaplax: absent (0); present (1). (character 30 in Appendix 1)

    9. Postero-dorsal granulations: absent (0), present (1)

    10. Shape of the shell: tapered (0); moderately low (1); subglobose (2).

    11. Position of the umbo: one third of the shell length (0); one fourth of the shell length (1).

    12. Shape of posterior part: lanceolate (0); subtruncated (1).

    Appendix 4

    Data matrix of 16 taxa and 12 characters employed for the cladistic analysis of the subgenus Barnea (Anchomasa).

    Stefano Monari "Phylogeny and Biogeography of Pholadid Bivalve Barnea (Anchomasa) with Considerations on the Phylogeny of Pholadoidea," Acta Palaeontologica Polonica 54(2), (1 June 2009).
    Published: 1 June 2009
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