Type genus: Polychaetura Kozłowski, 1956, younger synonym of Pteropelta Eisenack, 1939.

Discussion.—The family-level classification of Palaeozoic eunicidans was delineated by Kielan-Jaworowska (1966). The monotypic family Polychaeturidae was established particularly on the basis of the distinct carriers, left MI, the basal plate and anterior maxillae (Kielan-Jaworowska 1966: 102). The general labidognath apparatus architecture of polychaeturids is nevertheless similar to that of polychaetaspids and ramphoprionids. Therefore, Kozur (1970) regarded Polychaeturidae as a synonym of Polychaetaspidae, and placed Pteropelta as a genus of the latter family. Edgar (1984) emended the diagnosis of the Polychaetaspidae to incorporate four genera (from three families sensu Kielan-Jaworowska 1966); Ramphoprion, Oenonites (= Polychaetaspis), Kozlowskiprion, and Pteropelta (= Polychaetura). Later Orensanz (1990) also supported that idea and used Polychaetaspidae sensu lato in his jaw-based phylogenetic analysis of extant and fossil eunicemorph polychaetes.

In our opinion polychaetaspids and ramphoprionids represent well-constrained phylogenetical groupings, each possessing distinct morphological characteristics. Moreover, since Kielan-Jaworowska's (1966) monograph and the amendments subsequently suggested by Kozur (1970), Edgar (1984), and Orensanz (1990), additional genera have been described and assigned to both the Ramphoprionidae: “Pararamphoprion” Männil and Zaslavskaya, 1985, Protarabellites Stauffer, 1933, and Megaramphoprion Eriksson, 2001; and the Polychaetaspidae: Dubichaetaspis Eriksson, 1998 and Incisiprion Hints, 1998. If we now follow the amendments proposed by Kozur (1970), Edgar (1984), and Orensanz (1990) and lump all these genera—including Pteropelta—into Polychaetaspidae sensu lato, we would loose natural groupings of polychaetaspids and ramphoprionids and a useful rank in the classification hierarchy of fossil polychaetes would also become lost. A possible solution to the problem would be the application of an additional taxonomic rank, either subgenus or subfamily. Subgenera of fossil eunicidans have already been used by Bergman (1989) for paulinitids. His subgenus concept was, however, much narrower than would be in case of e.g., Dubichaetaspis, Incisiprion, or Megaramphoprion. Introduction of a subfamilial level (i.e., Polychaetaspinae, Ramphoprioninae, Polychaeturinae) could be more suitable. However, only a fraction of the early Palaeozoic jaw-bearing polychaetes is currently described and although Ordovician and Silurian faunas of Baltica and Laurentia are relatively well studied, those of other terranes are poorly known (see details in Hints and Eriksson 2007a). Therefore, many new genera and probably also families will be identified and described in the future. This may, in turn, considerably alter our view on the higher-level classification of early Palaeozoic jaw-bearing polychaetes. For these reasons we consider changing the classification of Kielan-Jaworowska (1966) premature and prefer, for the time being, to retain using Polychaeturidae at the family level.

Type species: Pteropelta gladiata Eisenack, 1939; Ordovician, Baltic region.

Discussion.—The genus Pteropelta was erected by Eisenack (1939) for isolated carriers of bifurcate morphology (the carriers comprise the posteriormost elements of the maxillary apparatuses; for a review of the general architecture of polychaete jaw apparatuses see, e.g., Kielan-Jaworowska 1966; Szaniawski 1996). Eisenack (1939) diagnosed Pteropelta as carriers with short median peaks (Medianhöcker in German), situated in the proximal part, and lateral spines (Lateralstacheln in German) with two posteriorly directed wing-like excrescences on the sides. In that same paper he described three new species: Pteropelta gladiata, P. thomsoni, and P. glossa, of which the first was designated as type species.

In 1956, Kozłowski described an articulated jaw apparatus, possessing carriers morphologically identical to those of Pteropelta, and named it Polychaetura gracilis. Kozłowski noted that with regard to the species of Pteropelta distinguished by Eisenack (1939), Pteropelta thompsoni seems to correspond to the carriers of Polychaetura gracilis. Thus Kozłowski (1956) apparently did not fail to notice the great similarity between Pteropelta and his new genus Polychaetura. He did, however, share the belief of Lange (1947, 1949) that the isolated elements (scolecodonts) are of little taxonomical value and that a different set of names had to be applied for articulated apparatuses.

Subsequently Kielan-Jaworowska (1966) obtained additional jaw apparatuses and numerous isolated elements belonging to Polychaetura, and erected a monogeneric family Polychaeturidae, which included two species; Polychaetura gracilis and Polychaetura sp. a (the latter has subsequently been described as Pteropelta kielanae, see below). She also noted the similarity between the carriers of Polychaetura and the scolecodonts described as Pteropelta by Eisenack (1939). Nonetheless, for the same reasons as Kozłowski (1956) she did not consider them as congeneric (discussed in closer detail by Kielan-Jaworowska 1968).

Tasch and Stude (1965), referring to the rules of the International Code of Zoological Nomenclature (ICZN), regarded eight apparatus-based generic names, Polychaetura included, as junior synonyms to Eunicites Ehlers, 1868. The latter amendment was erroneous and strongly criticised by KielanJaworowska (1968). Moreover, Jansonius and Craig (1971) suggested abstaining from assigning fossil polychaete jaws under the generic name Eunicites because of the very poor preservation of the type specimen of its type species.

Kozur (1970) was first to regard Polychaetura as a junior synonym to Pteropelta. For the emended diagnosis of Pteropelta, he proposed to use those provided by Kozłowski (1956) and Kielan-Jaworowska (1966) for Polychaetura. The question of the type material was, however, left open and Kozlowski's (1956) species P. gracilis was kept separate from those described by Eisenack (1939). Perhaps due to the strong criticism on Kozur's (1970) work (e.g., Jansonius and Craig 1971; Szaniawski and Wrona 1973), several authors were reluctant to use Pteropelta as opposed to Polychaetura. Edgar (1984) provided a cursory discussion on the element-based versus apparatus-based classification with regards to polychaeturids. He did not consider those two generic names as synonymous, but preferred to maintain both classification systems. Hints (1998) also used Polychaetura instead of Pteropelta but noted that some of the names employed may turn out to be junior synonyms. More recently, Hints (2000), Hints and Eriksson (2007a), and Eriksson and Hints (2009) have illustrated a few polychaeturid jaws (MI, basal plate and carriers) under the generic name Pteropelta.

Eisenack's (1939) collection, including the type material of Pteropelta, was obtained in the 1930s but became lost during World War II. Neotypes have subsequently been designated for several species of chitinozoans, foraminiferans, and acritarchs (e.g., Eisenack 1959), but not for scolecodonts. With respect to the diagnostics and applicability of a genus, the validity of the type species and its corresponding type specimen are of particular significance. Thus designation of a neotype for Pteropelta gladiata is a prerequisite for solving the above described synonymy problem.

The International Code for Zoological Nomenclature recommends that neotypes should derive from a horizon and locality as close as possible to that of the holotype (ICZN; Article 75). In the case of Pteropelta this is complicated because Eisenack's (1939) material came from erratic boulders found in Germany, but with a Baltic provenance. The precise age of these boulders are not known, but most likely they are of Ordovician age. Eisenack's (1939) type specimen of Pteropelta gladiata is morphologically identical to the carriers of the type specimen of Polychaetura gracilis (a well preserved apparatus illustrated by Kozłowski 1956: fig. 17), except being larger. Like Eisenack's (1939) material, Kozłowski's (1956) type specimen was derived from an erratic boulder, the specific age of which is ambiguous. However, the entire apparatus, complemented with isolated jaws recovered from the same boulder, provides much better basis for taxonomy than the single carriers. Considerable variation in size of the jaws of P. gracilis was noted by Kielan-Jaworowska (1966: 105) and confirmed by the present authors to be regarded as intraspecific variability. We therefore believe that Pteropelta gladiata and Polychaetura gracilis represent one and the same species and designate the holotype of Polychaetura gracilis as neotype for Pteropelta gladiata, thus also making the former name a junior synonym of the latter.

Concerning the two other species of Pteropelta described by Eisenack (1939), the single specimen of Pteropelta glossa is regarded to be conspecific with Pteropelta gladiata. The main difference between the two is the shape of the shaft, which is narrower in P. gladiata. The shaft is, however, very thin along the longitudinal axis and its shape thus depends largely on the state of preservation.

We agree with the opinion of Kozlowski (1956: 197) and Kielan-Jaworowska (1966: 102), that Pteropelta thompsoni is conspecific with P. gladiata. However, one of the specimens assigned to P. thompsoni by Eisenack (1939: pl. B: 2, specimen No. 3), has an anterior margin that is nearly straight or slightly convex as opposed to being distinctly concave in those of P. gladiata. Similar carriers are found in P. huberti described below. The carriers of P. kielanae (Hints, 1998) and Pteropelta sp. A herein are hitherto unknown, but their left MI share similar, straight posterior margins. Accordingly the anterior margins of the carriers (which fit with the posterior terminations of the MI) of all three species are also expected to be similar. Two of the P. thomsoni specimens (including No. 3) were not recovered from an erratic boulder but from an outcrop in Rakvere town (formerly Wesenberg) of northern Estonia. Eisenack (1939: 165) noted that they were derived from “Stufe D_11”, which corresponds to the Keila Regional Stage. This age determination nevertheless remains ambiguous since most of Rakvere town is actually confined to the outcrop area for strata belonging to the Rakvere Stage. This uncertainty interval, from the Keila to Rakvere stages, overlaps with the known ranges of the three above mentioned species and therefore specimen No. 3 of Eisenack (1939) could belong to any of these.

In conclusion, studies of appropriate type material as well as new scolecodont collections have supported the taxonomic amendment originally proposed by Kozur (1970). The name Polychaetura Kozłowski, 1956 is regarded as a junior synonym of Pteropelta Eisenack, 1939, and Polychaetura gracilis Kozłowski, 1956 as a junior synonym of Pteropelta gladiata Eisenack, 1939.

1939 Pteropelta gladiata sp. nov.; Eisenack 1939: 164, pl. C: 2.

1939 Pteropelta glossa sp. nov.; Eisenack 1939: 164, pls. B: 1, C: 2–3.

1939 Pteropelta thompsoni sp. nov.; Eisenack 1939: 165, pl. B: 3.

1956 Polychaetura gracilis sp. nov.; Kozłowski 1956: 192–195, figs. 17–18.

1956 Polychaetura sp. a; Kozłowski 1956: fig. 19.

1966 Polychaetura gracilis Kozlowski; Kielan-Jaworowska 1966: 103– 105, pls. 22, 23: 3–7, text-fig. 8L.

1982 “Zusammengesetzte Maxille links”; Schallreuter 1982: pl. 2: 5.

1996 Polychaetura gracilis Kozłowski; Szaniawski 1996: pl. 2: 6.

1998 Polychaetura gracilis Kozłowski; Hints 1998: 496, fig. 12A–D.

2000 Pteropelta gladiata Eisenack; Hints 2000: pl. 2: 3–4.

2007 Pteropelta gladiata Eisenack; Hints and Eriksson 2007a: fig. 4F–G.

2009 Pteropelta gladiata Eisenack; Eriksson and Hints 2009: fig. 5k–l.

Type material: Holotype: carriers figured by Eisenack 1939: pl. C: 2 (specimen lost), neotype: apparatus (ZPAL Sc 0/1/1) figured by Kozlowski 1956: fig. 17.

Type locality and horizon: Erratic boulder No. 0.116 of Baltic origin, Upper(?) Ordovician age, collected from Wyszogród, Poland.

Remarks.—This species has been described in detail by Kozlowski (1956) and subsequently also by Kielan-Jaworowska (1966). In one of the articulated apparatuses recovered (Fig. 1U) we discovered anterior maxillae with an unusual morphology. At least the right MII, but possibly also the MIV and the left MII appear to be composed by lamella-like plates, each one terminating dorsally into a denticle. Similarly, Kielan-Jaworowska (1966: 104–105) noted in the description of Polychaetura gracilis that the boundaries between the denticles of the anterior maxillae are prolonged along the entire width of the jaw and (for the left MIII) that the jaw becomes separated into individual denticles. Such type of anterior maxillae is characteristic of Tretoprion astae Hints, 1999 and may suggest a relationship between the Polychaeturidae and Tretoprionidae (see also discussion of Pteropelta kielanae below).

Based on the extensive collections from Estonia Pteropelta gladiata is the only polychaeturid species, which has incised posterior margin in left MI and concave (incised) anterior margins of carriers.

The variability of P. gladiata is relatively wide concerning both size (cf. Fig. 1_O and J₁) and general morphology of the posterior maxillae (see for example specimens in Fig. 1C and D which are from the same sample). In addition, there is a notable morphological trend within the lineage. In the left MI this concerns the inner wing, which is relatively wider in Darriwilian to early Katian specimens (Fig. 1A–G) compared to younger material (Fig. 1H, I). Generally, the right MI becomes more elongated with a longer shank and reduced ramus (cf. Fig. 1L and P). Like Kielan-Jaworowska (1966) we consider these differences to fall within the intraspecific variability. It should be added that the proposed neotype represents the older morphotype of the species.

Stratigraphic and geographic range.—Volkhov to Juuru regional stages (Darriwilian to basal Llandovery) of Baltoscandia (Estonia, NW Russia, Sweden, Poland), Baltic erratic boulders, upper Richmondian (Katian) of Ohio, USA; possibly Ordovician(?) of Kazakhstan.

1966 “Polychaetura” sp. a; Kielan-Jaworowska 1966: 105–106, pl. 23: 1, 2.

1998 Polychaetura kielanae sp. nov.; Hints 1998:497–498, figs. 12H–L.

2000 Pteropelta kielanae (Hints); Hints 2000: pl. 2: 8.

Emended diagnosis.—Hints (1998: 498) diagnosed this species as differing from Polychaetura gracilis in having wider posterior maxillae (MI), a left MI with straight instead of incurved posterior margin and a longer inner wing. It differs from P. gracilis, P. huberti, and Pteropelta sp. A in having a right MI with sub-rectangular instead of triangular outline of the shank.

Remarks.—Hints (1998: fig. 12H) illustrated a fused right MII and MIV from this species in which the same feature as discussed above for Polychaetura gracilis can be observed, i.e., that the individual denticles of these anterior maxillae are weakly fused and their boundaries continue through the element providing a lamella-like appearance. Whether or not P. huberti and Pteropelta sp. A also have similar anterior maxillae is presently not known. If this proves to be a feature typical for all polychaeturids their supposedly close relationship to polychaetaspids and ramphoprionids (Kielan-Jaworowska 1966) may need reconsideration.

Stratigraphic and geographic range.—Pteropelta kielanae is most common in the Haljala and Keila stages (Sandbian to basal Katian) of Estonia and NW Russia. Questionable finds derive from the Uhaku Stage (upper Darriwilian) of Estonia and Kukruse Stage (basal Sandbian) of south-eastern Sweden (MEE, unpublished data).

1998 Polychaetura sp. A; Hints 1998: 498–499, figs. 12E–G.

2000 Pteropelta sp. A; Hints 2000: pl. 2: 1, 2.

Etymology: Named in honour of Hubert Szaniawski in recognition of his work on fossil scolecodont-bearing polychaetes.

Type material: Holotype: left MI, GIT 592-1, Fig. 2X; paratypes: GIT 592-2 to 592-26.

Type locality: Lelle D-102 borehole, central Estonia.

Type horizon: Vormsi Regional Stage (Katian).

Material.—Several hundred right and left MI, ca 50 basal plates, and seven pairs of carriers from Laeva 18, Lelle D-102, Rapla and Orjaku drill cores and Viru mine section.

Diagnosis.—Posterior maxillae of Pteropelta huberti are most similar to those of P. kielanae. The main differences concern (i) outline of the shank, which is sub-triangular in P. huberti, but sub-rectangular in P. kielanae; (ii) inner wing in left MI, which is longer in P. huberti and with more slanting anterior margin; (iii) dentary in left MI, where the largest denticle is the second or third in P. huberti instead of fourth or fifth as in P. kielanae. Pteropelta huberti differs from P. gracilis in having almost straight posterior margin in left MI and straight or slightly convex anterior margin in carriers. P. huberti commonly differs from other species of Pteropelta also in having two anteriormost denticles in both MI transversally extended.

Description.—Right MI: L = 0.3–1.2 mm, L/W ratio = 2.0– 3.0. Anterior half of jaw considerably wider than posterior half. Outer-lateral margin is almost straight or with a small incurvature in the middle. Sub-rounded, more or less club-shaped ramus extends to 0.43–0.55 of jaw length from anterior. Bight more or less anteriorly concave; in smaller specimen it may be almost transverse and perpendicular to length axis. Outer margin along the shank is directed posteriorly in the first half of the shank, then it bends continuously and is directed towards the end of the dentary. Posteriormost termination generally developed into a small tubercle. Dentary comprises 11–17 sub-conical denticles, first three (particularly first two) of which may be prolonged transversally into short ridges. Denticles rather tightly packed and decrease gently in size particularly posterior of midlength where they are also more slanted. Posteriormost part of dentary commonly slightly dextrally bent. Inner margin sub-parallel to dentary and inner face is steep. Anteriorly inner face widens slightly, forming a more or less distinct inner wing that extends for approximately 0.9 of jaw length. Anteriormost termination of inner wing forms a more or less well-developed cove, anterior of which the inner face is very narrow in dorsal view. In ventral view the myocoele is almost gaping with a cover extending for 0.05–0.07 of jaw length.

Left MI: L = 0.33–1.1 mm, LAV ratio = 2.0–3.1. Sub-rectangular jaw with its widest part usually just anterior of midlength. Outer margin runs most often postero-laterally for 0.4–0.5 of jaw length, where it bends and continues towards the denticulated ridge, and then continues sub-parallel to dentary until it meets the posterior margin. Sometimes a small bight, similar in extension to that in right MI, can be seen. Below the ramus the edge of the outer face is thinner and less sclerotised which sometimes gives the outer margin a ragged, semi-translucent appearance. Such specimens in particular resemble the morphology of the ramus and bight of the right MI. Long, almost rectangular inner wing reaching to 0.70–0.75 of jaw length from posterior with an inner margin sub-parallel to dentary. Relatively wide, almost straight and transverse posterior margin forms 0.35–0.50 of jaw width. Dentary consists of 10–15 denticles, three first ones may be prolonged transversally like in right MI. If not prolonged, the first two are smaller than the third denticle. Dentary particularly elevated on a ridge in posterior half of jaw. In ventral view, myocoele is almost gaping, cover extends to approximately 0.05 of jaw length. Small denticle pits visible in the narrow furrow that corresponds to the dentary and which widens anteriorly.

Basal plate: Sub-trapezoidal element approximately half as long as right MI. L = 0.35–0.8 mm, LAV ratio varies from 2.0 to 3.3. Inner margin is longer than outer margin. In dorsal view, posteriormost termination usually has posteriorly-directed, narrow and blunt extension. Dentary houses 10–18 subtriangular denticles of which the anteriormost generally is the largest one. In ventral view, cover comprises 0.5–0.7 of jaw width.

Carriers: Fused carriers are about 2.2 times longer than wide. The shaft of a single carrier has two posteriorly directed branches, the proximal one being 3 times longer than the distal one. Anterior margin of carriers are nearly straight.

Variability.—The outline, especially the length/width ratio varies considerably in the first maxillae. The anteriormost denticles of these elements, moreover, may be developed into short transverse ridges. In the basal plate, two types of denticulation occur: (i) all denticles are relatively large and of nearly equal size and shape, and (ii) anteriormost denticles are smaller and/or more slender than the remaining ones.

Remarks.—The development of the anteriormost denticles in the MI into transverse ridges is unique for Pteropelta huberti among the polychaeturids, but similar denticles are not uncommon for Ordovician scolecodonts. Two examples, where such ridges are developed in extreme form are seen in the jaws of Rhytiprion magnus Kielan-Jaworowska, 1966 (cf. Bergman et al. 2003) and Kaljoprion laevaensis Hints, 2008. Moreover, the long-ranging Tretoprion astae Hints, 1999 and a species of Pistoprion (Kielan-Jaworowska 1966: pl. 7: 1 ; Hints 2000: pl. 1: 2) possess similar ridges in their maxillae. Thus taxa having different types of jaw apparatuses (placognath and labidognath) could develop such denticles. Only in the case of P. huberti, however, the lack or presence of this feature can be considered as falling within the range of the intraspecific variability. It is noteworthy that the ridges in P. huberti are well developed only in specimens occurring in the uppermost part of its stratigraphical range (Vormsi and Pirgu stages, upper Katian), where it co-occurs with R. magnus, K. laevaensis, and T. astae. It is therefore likely that the development of such denticles in P. huberti had functional advantage, perhaps for certain types of diet or burrowing.

Stratigraphic and geographic range.—Pteropelta huberti ranges from the Uhaku to Pirgu regional stages (Darriwilian to Katian) in Baltoscandia and Poland, being most characteristic of the Nabala and Vormsi stages (middle Katian).

2009 Pteropelta sp.; Eriksson and Hints 2009: fig. 5m, o (n tentatively).

Material.—Three right MI, three left MI, two Bp from the Saku quarry and the Vasalemma 758 borehole of Estonia and the Stormyr-2 and Båticke-3 boreholes of Sweden.

Description.—Right MI: L = 1.0–1.2 mm, LAV ratio = 2.3– 2.5. Outer margin runs straight postero-dextrally and just above mid-length bends, enclosing a sub-rounded ramus extending to approximately 0.5 of jaw length from anterior; bight, vaguely concave anteriorly. Posterior of ramus outer face comparably wide, tapering gently and evenly. Posteriormost termination of jaw bluntly subtriangular and dorso-ventrally compressed compared to the elevated denticles. Dentary houses 18–19 tightly packed denticles that decrease evenly in size posteriorly. Fourth and sixth denticles may be slightly smaller than surrounding ones. Anterior part of dentary arranged sub-transversally to length-axis. Elevation of the dentary more pronounced in anterior half of jaw. Inner face is narrow and steep, very narrow inner wing representing c. 0.85 of jaw length may be visible. In ventral view cover comprises 0.1 of jaw length.

Left MI: L = 0.75–1.6 mm, LAV ratio = 2.2–2.9. Sub-rectangular sturdy jaw with wide, nearly straight transverse posterior margin. Outer margin runs straight postero-sinistrally and bends at approximately 1/3 to half of jaw length, sometimes enclosing a relatively narrow ramus-like feature, and continuing postero-dextrally and sub-parallel to dentary in posterior half of jaw. Dentary houses 16–18 sub-triangular, relatively tightly packed denticles. First three denticles arranged sub-transversally to length axis and decrease evenly in size, following one or two are considerably smaller whereas the next one is as big as the first denticle. Posterior of this, denticles decrease evenly and gently in size. Denticulated ridge particularly elevated and well-developed in posterior half of jaw. Long, sub-rectangular inner wing extending for 0.65–0.77 of jaw length. Its inner margin is straight and parallel to dentary. Anterior of inner wing, inner face is not visible in dorsal view. In ventral view cover comprises approximately 0.1 of jaw length.

Basal plate: Sub-trapezoidal element. L= 0.36–0.58 mm, LAV = c. 2.2. Inner margin is longer than outer margin. Anterior margin wider than posterior one. Posteriormost termination usually has posteriorly-directed, narrow and blunt extension. Dentary houses 12–14 sub-triangular denticles which are slightly bigger in posterior half of jaw.

Remarks.—Although this species is distinctive and differs from all other polychaeturids, it is here kept under open nomenclature because of the limited amount of material available. The jaws of Pteropelta sp. A are most similar to those of P. kielanae. The main difference in the right MI is the shape of the posteriormost termination; the undenticulated ridge is longer and somewhat pointed in Pteropelta sp. A, as a posterior continuation of the outer face. The few jaws hitherto recovered of Pteropelta sp. A are, moreover, bigger and have an over-all sturdier appearance than to those of P. kielanae. The MI dentary of Pteropelta sp. A is more differentiated (especially in the left MI where small, intermediate denticles occur) and has more denticles than that of P. kielanae. By contrast to the other polychaeturids that have a left MI most reminiscent of those of the polychaetaspid genus Oenonites, the left MI of Pteropelta sp. A has a general morphology superficially resembling those of certain ramphoprionids (Protarabellites) or even kalloprionids (see, e.g., Eriksson 2001, 2006). See also discussion by Kielan-Jaworowska (1966: 102–103).

Stratigraphic and geographic range.—Pteropelta sp. A is recorded from the Keila and Oandu stages (lowermost Katian) of northern Estonia and from the Pirgu Stage (upper Katian) of Gotland, Sweden.