Revision of South African Caecidae (Mollusca: Gastropoda)

ABSTRACT The South African species of Caecidae are revised on the basis of the material stored in the KwaZulu-Natal Museum (Pietermaritzburg, South Africa). Twenty species are recognized, 10 of which are described as new: Caecum austrafricanum, C. incisum, C. intortum, C. Knysnaense, C. leilae, C. lindae, C. maraisi, C. morgan, Parastrophia avaricosa and P. ornata. The lectotype of Caecum subquadratum Carpenter, 1859 is herein selected.


Terminology
Cutting plane -plane delineated by the edge of the shell at the apex (excluding septum and mucro); septum -closure of the shell after the previous stage is discarded; mucro -appendage often visible on the septum; dorsal side -convex side of the tube; ventral side -concave side of the tube; left and right side are referred with respect to the ventral side; macula -spot placed in the middle of the ventral side of the tube; coiled protoconch -the first portion of the protoconch in the subfamily Pedumicrinae; uncoiled protoconch -the uncoiled section of the protoconch in the subfamily Pedu micrinae following the coiled protoconch, clearly distinct from the teleoconch, from which it is mostly separated by a varix. All type material of the new species is stored in the NMSA, unless otherwise stated. Species identification is based solely on shell and operculum morphology.
Caecum subquadratum Carpenter, 1859 Figs 1A-I, 3, 21E, 22A-C, 23A-C, 26G-I Caecum subquadratum Carpenter, 1859: 433. Caecum subquadratum: tryon 1886: 216. Caecum subquadratum: Hedley 1914. Caecum subquadratum: Pizzini & Raines 2011: 28, fig. 3H. type locality: SOUtH AFRICA: Port Elizabeth, here amended (see under remarks). type material examined: Lectotype herein selected (NHMUK 1858.12.9.13, Fig. 21E), glued on a small glass slide labelled by the author with white ink and a paper label, specifying the origin from Bean's colln ( Original description: "33 ? Caecum subquadratum, n. s. ? Caecum (Fartulum) t. elongata, minima, laevi, haud nitente; apertura haud contracta; septo submamillato, subungulato; margine laterali extante, supra satis convexo, lateribus rectis, parallelis; apice obtusissimo, lato, ad latus quadrato: operculo? ... Long. .068, Additional description: tube cylindrical, slender, slightly arched, whitish to transparent, in beached specimens often with alternating white and semitransparent bands, without sculpture. Aperture simple, sometimes with a barely visible swelling. Surface dull, smooth, featureless. Septum opaque, dome-shaped, very protruding. Mucro nail-like, rotated toward the right side, as high as the septum. When viewed from the right side the septum shows a subquadrate outline, while in ventral view it is bigibbous. Periostracum colourless. Juveniles are similar to the adults, and are distinguished by the subcylindrical and more arched tube, and by the less protruding septum and proportionally higher mucro which shows a more rounded lateral outline. Larval stage unknown. Operculum thin, corneous, circular, multispiral, composed of a central nucleus surrounded by a tight spiral of 4-5 whorls. External side slightly concave, internal side with a raised central disk (Fig. 1C). Length: 1.6-1.9 mm. Distribution: Southwestern to eastern coast of South Africa, from Saldanha to Port Edward (Fig. 3). Remarks: Although the type locality of this species seems to be clearly indicated, i.e. Port Elizabeth, both the synopsis at the end of Carpenter's paper (1859: 443) and the original label of the lectotype refer to Australia (Fig. 21F). However, there is no toponym that refers to a Port Elizabeth in Australia. Conversely, a well-known Port Elizabeth exists in South Africa, hence one can suspect some confusion by Carpenter. Nevertheless in the introduction of his paper, Carpenter (1858: 417) clearly states that he could not find any Caecum species "at the Cape, or at Port Natal [today Durban]", so one can deduce that he did not examine any Caecidae from South Africa. Moreover, C. subquadratum is the only Australian species reported in his paper. this ambiguity was also noticed by Hedley (1914), who reported a drawing of the lectotype but no Australian records. Furthermore, there is no specimen in either the AMS or WAM collections ascribable to subquadratum. Despite the uncertainty of the type locality, C. subquadratum is a well- defined species, characterized by a slender, cylindrical tube and by the squared profile of the septum in lateral view, while in ventral view it is more or less bimamillated. South African specimens perfectly fit the lectotype, except for the length of the tube. In fact, some populations are notably longer than the lectotype, suggesting that it is a subadult shell. On the basis of the available information the type locality of C. subquadratum is here amended as: SOUtH AFRICA: Port Elizabeth.
Caecum morgan sp. n. Figs 2A-F, 3, 22D, E, 23D, E, 26J, K Etymology: Derived from the type locality (Cape Morgan) and used as a noun in apposition. Description: tube small, subcylindrical, proportionally thick, whitish, smooth. Aperture slightly oblique toward the ventral side, showing a well-developed swelling followed by a contraction and finally by a very small ring. Surface smooth, dull, without microsculpture. Septum opaque, slightly protruding over the cutting plane, with a sharp, nail-like mucro directed toward the right side, giving a dome-shaped outline to the septum when viewed from the side. Early stages and operculum unknown.  Raines & Pizzini, 2005, holotype (LACM 3027); C. chinense de Folin, 1868, lectotype (MNHN-IM-2000; C. dakuwaqa Pizzini, Raines & Vannozzi, 2013, holotype (MNHN-IM-2000; C. subquadratum Carpenter, 1859, lectotype (NHMUK 1858; C. fijiense Pizzini, Raines & Vannozzi, 2013, holotype (MNHN-IM-2000. Distribution: Currently known only from the type locality, Cape Morgan, north of East London (Fig. 3). Remarks: Caecum morgan sp. n. strongly resembles C. subquadratum due to the lack of both sculpture and microsculpture, as well as a similar shape of the mucro. It can however be separated by the distinctly subcylindrical and more curved shape of the tube, and by the presence of a conspicuous swelling above the aperture, barely visible in C. subquadratum. In C. morgan sp. n. the septum is only somewhat emerging above the cutting plane. Conversely, in C. subquadratum the septum is more protruding, on the whole giving the mamillate-ungulate appearance pointed out by Carpenter (1859). Caecum morgan sp. n. resembles C. gofasi Pizzini & Nofroni, 2001 in general aspect, but the latter has a dorsal spatulate mucro and shows a distinct worm-like microsculpture absent in the new species. Moreover, C. morgan sp. n. is also similar to C. campanulatum Pizzini 2005, C. dakuwaqa, andC. fijiense (both Pizzini, Raines &Vannozzi, 2013), having the same bell-shaped aperture, but in these species the septum is domeshaped without any mucro. Additionally, C. morgan sp. n. differs from C. dakuwaqa by the lack of the exasperate torsion of the tube occurring in the latter. Caecum morgan is also similar to C. musorstomi Pizzini, Raines & Vannozzi, 2013, from which it can be separated by the smooth surface without sculpture, and microsculpture and by a different orientation and shape of the mucro.
Caecum austrafricanum sp. n. Figs 4A-H, 7, 22F-H, 23F-H, 24A, 25N, O Etymology: From Latin name auster (the south) and the adjective africanus (African), meaning South African. Description: tube subcylindrical, slender, with a slight dextral torsion, rather straight in the adapical portion, more or less curved in the abapical half. tube smooth, somewhat glossy, colourless. Aperture oblique with a rather strong swelling, preceded by a white band. Surface with only oblique growth lines. Septum opaque, protruding, with a variable outline, often from flat to Sshaped, more rarely convex, with a dorsal nail like mucro, somewhat rotated toward the right side, generally more protruding than the septum. Macula large with a frosted appearance, more or less symmetrical, elongated, placed in the middle of the ventral side, posteriorly bilobed, anteriorly narrower and fading.   Distribution: Southern and eastern coasts of South Africa, from False Bay to Aliwal Shoal, south of Durban (Fig. 7). Remarks: this species is rather variable in terms of dimensions and curvature of the tube, which is, however, always straighter in the middle portion. the most similar species to Caecum austrafricanum is C. variegatum de Folin, 1867 (Fig. 21A-D). Caecum variegatum was originally described by de Folin from Hong Kong and recently reported by Hughes (1985) for the same locality, while no other finding is reported in the literature. this species seems to be absent from Australia as well (unpublished data). the main differences concern the absence of apertural swelling in C. variegatum and the shape of the mucro, which is narrow and spatuliform in C. variegatum, while in C. austrafricanum it is broad and not distinct from the septum when observed in ventral view (Figs 21D, 23F, G).
Caecum austrafricanum resembles C. macrum van der Linden & Moolenbeek, 2000 ( Fig. 25R) described from western Africa, from which it can be distinguished by the slenderer and thicker tube, the aperture provided with a well-developed swelling not observed in C. macrum and by the different shape of the septum. Moreover, the macula in C. macrum is different, being shorter and heart-shaped (Fig. 24A, H).
Caecum knysnaense sp. n. Figs 5A-E, 7, 22I, 23I, 24B, 25P Etymology: Derived from the type locality. Description: tube subcylindrical, with a slight dextral torsion, evenly arched. tube smooth, glossy, colourless, semitransparent. Aperture with a barely visible swelling, strongly oblique toward the ventral side, preceded by a white band. Surface with only fine oblique growth lines. Septum smooth, domeshaped, protruding, with an earlike mucro directed halfway between the dorsal and the right side. Macula large, with a frosted appearance, formed by two oblong bands fused in the middle. Juveniles rather similar to the adults, showing a narrower and more arched shape of the tube. Periostracum light brown. Operculum flat with a raised internal nucleus and internally thickened edge. Distribution: Known with certainty only from Knysna (Fig. 7). Remarks: this species clearly resembles Caecum austrafricanum sp. n. However, there are some consistent differences that set specimens of this species apart from the hundreds of C. austrafricanum specimens found in the same sites. In fact, C. knysnaense sp. n. is smaller and shows an aperture which is more oblique by ca. 10° and lacks a clear swelling. Additionally, the septum of C. knysnaense is convex while in C. austrafricanum it is typically flat or Sshaped. Also the mucro and the general aspect of the tube are different.
Caecum knysnaense also strongly resembles C. macrum van der Linden & Moolenbeek, 2000 ( Fig. 25R), from which it can be distinguished by the different shape of the mucro and by the more oblique aperture. Also the macula is different, being shorter and heartshaped in C. macrum (Fig. 24B, H).

Caecum intortum sp. n.
Figs 6A-F, 7, 22J, 23J, 24C, D, 25Q Etymology: From the Latin adjective intortus (= twisted) due to the twisted shape of the tube. Description: tube cylindrical, only slightly arched. the tube shows a clear dextral torsion. tube smooth without sculpture, colourless, dull. Aperture preceded by a slight swelling. the aperture is oblique in both ventral and lateral direction, being contracted on the left side. Surface with only oblique, fine growth lines. Septum domeshaped, granulated, with a broad nail-like mucro directed toward the right side. Macula large, illdefined, expanded, with a frosted appearance, clearly displaced to the left side. Juveniles rather different from adults, more conical and showing a clear dextral torsion. Larval stage not determined with certainty, probably with a multispiral protoconch. Periostracum light brown. Operculum, corneous, circular, multispiral, composed of a small central nucleus surrounded by an open spiral of 67 whorls. External side flat, internal side with a concave nucleus.  Distribution: Southern coast of South Africa from Hermanus to Algoa Bay (Fig. 7). Remarks: the species most similar to Caecum intortum is C. crassum de Folin, 1870 (Fig. 25S, t), an endemic species of western African coasts (from West Sahara to Ghana), having in common the general shape of the tube and the typology of the septum, but differing in the smaller dimensions and in the exasperate torsion of the tube not observed in C. crassum. Additionally, C. intortum shows a different shape of the macula, which is also clearly displaced toward the left, and lacks the longitudinal microsculpture that is observed in C. crassum (van der Linden & Moolenbeek 2000). Caecum intortum resembles both C. austrafricanum sp. n. and C. knysnaense sp. n., from which it can be separated by a wider tube, a more cylindrical shape, a clearly twisted tube and the position of the mucro, lateral rather than dorsal.  Description: tube cylindrical, evenly arched, smooth without sculpture. Both tube and septum are semitransparent, colourless and glossy. Aperture simple, without any swelling or varix, even and not oblique. Microsculpture comprised of collabral incisions which define flat rings. These incisions, spaced by about 2-3 µm apart and rather regular in young specimens, tend to become irregular in adults. this feature causes the appearance of the shells, glossy and shining in the former, to become milky and opaque in the latter. Septum smooth, dome-shaped, with an ear-like mucro rotated toward the right by about 45°. the septum shows some more or less parallel grooves arranged like waves coming from the tip of the mucro. In terms of both curvature of the tube and shape of the aperture juveniles are quite similar to the adults, and are distinguished by the smaller diameter and the more regular microsculpture. Periostracum colourless, dull. Larval stage and operculum unknown. Distribution: Southern and eastern coasts of South Africa from Knysna to Aliwal Shoal (Fig. 11). Remarks: the microsculpture exhibited by C. incisum is unique among South African Caecum species. this kind of microsculpture is shown by C. sinuatum de Folin, 1867 described from Borneo. However, de Folin's species is quite different from C. incisum, showing a very slender and slightly arched tube, a different shape of the septum and a strong constriction before the aperture. Caecum incisum occurs sympatrically with C. austrafricanum sp. n., C. intortum sp. n. and C. inhacaense, from which it can be distinguished by the even curvature of the tube, the lack of apertural swelling, the presence of incised growth lines defining flat rings throughout the tube, the lack of the macula and the different shape of the mucro. Description: tube small, slightly subcylindical, more arched toward the aperture. Both tube and septum are semitransparent, colourless and glossy. the surface shows a microsculpture composed of shallow worm-like grooves interrupted by irregularly-set growth lines. At higher magnification, the microsculpture is composed of very small pits with a diameter of about 1 µm arranged in longitudinal rows. Septum vitreous, smooth, domeshaped, very protruding, with an indistinct mucro directed toward the right side. the septum shows some more or less parallel grooves arranged like waves coming from the tip of the mucro. Juveniles quite similar to the adults, and are distinguished by the more tapered shape, the smaller diameter and the less protruding septum. Larval stage and operculum unknown.  Distribution: Only known from the type locality and from Fish River mouth (between Port Alfred and East London) (Fig. 11). Remarks: this species strongly resembles C. incisum sp. n. which is found in sympatry and with which it is easily confused. It can be distinguished by the slenderness of the tube, the absence of ring-like growth lines, the presence of longitudinal microsculpture and by the different shape of the septum, which is more protruded and with a parabolic outline.

Caecum incisum
Caecum leilae sp. n. Figs 10A-N, 11, 22P, Q, 23P, Q, 24E, F, 26M-P Etymology: Named after the late Leila Zitelli, second author's mother. Description: tube rather large, cylindrical, colourless and glossy, semitransparent, evenly arched, sculptured by very fine, slightly oblique rings, more evident in the abapical half, separated by narrower interspaces. Aperture simple, contracted, slightly oblique toward the ventral side. Surface grooved by gross, shallow, worm-like incisions visible at low magnifications especially in the adapical half. Septum domeshaped, opaque, smooth, very protruding. Mucro ear-like, of variable height with respect to the septum, positioned at a variable angle between the dorsal and the right side. Surface of the septum with orange-peel aspect. Sparse, irregular grooves arranged like waves coming from the mucro are often visible on the septum. Macula small, heart-shaped, hardly visible, transparent, slightly displaced to the left side. Periostracum light brown, dull, easily lost, sculptured by fine longitudinal wormlike grooves. Juveniles quite similar to the adults, having the same morphology of the aperture, sculpture and microsculpture and are distinguished by the smaller diameter, the more curved tube, the less defined rings and by the slightly less protruding septum. Larval stage unknown. Operculum thin, corneous, circular, multispiral, composed by a small central nucleus surrounded by an initially tight spiral of 7-8 whorls. External side slightly concave, internal side with a slightly convex nucleus. Distribution: Eastern coast of South Africa from Mbotyi (south of Port Edward) to St. Lucia (Fig. 11). Remarks: Caecum leilae resembles C. inflatum de Folin, 1869 and C. attenuatum de Folin, 1880 which show a similar annulated sculpture, but the septum is different, with a larger and illdefined mucro in C. inflatum and with a triangular outline in C. attenuatum. Caecum leilae can also be compared with the IndoWest Pacific species C. cooki Pizzini & Raines, 2011 with which it shares the shape of the ear-like mucro, but shows no sculpture and a different shape of the aperture as well.
Juveniles of C. leilae can be confused with C. incisum and C. inhacaense. However, C. leilae can be distinguished by the different sculpture (obsolete rings in leilae, incised collabral grooves defining flat rings in incisum) and by the mucro (broader in C. incisum and by the presence of the longitudinal microsculpture, while the latter shows a different shape of the mucro and lacks the regular annular sculpture crossed by the longitudinal microsculpture occurring throughout the tube that is typical of C. leilae). Moreover, the maculae in C. leilae and C. inhacaense are different in both shape and colour (heartshaped and transparent in the former, roundish to chevron-shaped and opaque white in the latter) ( Fig. 24E-G).

Caecum inhacaense Albano & Pizzini, 2011
Figs 12A-C, 13, 22K, 23K, 24G, 26A, B   Additional description: tube cylindrical, colourless, whitish in beached specimens, the last portion bent toward the ventral side. No sculpture. Aperture slightly flaring and oblique. Surface with only oblique growth lines. Septum opaque, dome-shaped, variably protruding. Mucro illdefined, placed on the right side, typically higher than the septum, dorsally protruding with a resulting concave outline just above the cutting plane. Macula white, small, roundish to chevron-shaped, located in the middle of the ventral side of the tube, slightly displaced toward the left side (Fig. 24G). Periostracum light brown, somewhat glossy, persistent. Length: 1.2-1.6 mm. Distribution: Originally described from south of Mozambique, its distribution is herein extended to the eastern coast of South Africa up to the Mtentu River (Fig. 13). Its occurrence on the southern coast needs confirmation. Remarks: Caecum inhacaense resembles the sympatric C. incisum sp. n. as regards to the general proportions, but it can be distinguished by the presence of a white macula, the lack of incised collabral grooves, the presence of a slight apertural swelling and the mucro that forms a lower angle with respect to the ventral-dorsal direction. Caecum inhacaense is a rather elusive species due to the lack of striking characters. A careful examination of South African specimens revealed that the bending of the last quarter of the tube and the shape of the mucro are useful characters. In particular, the mucro is neither nail-nor ear-like as in other species with similar appearance, but has a convex outline, shaped like a flattened ball that protrudes dorsally, leaving a concave region just above the cutting plane. Also the presence of a small, white macula is a useful character.
Caecum cf. gulosum Hedley, 1899 Figs 13, 25F Material examined: SOUtH AFRICA: KwaZulu-Natal: 1 lv, Kosi Bay, main reef, 1-4 km S of estuary mouth, stone surfaces, ± -15 m, dived D. Herbert, 4.v.1990 (NMSA S2869). Description: tube evenly arched, colourless, semitransparent. Surface crossed by coarse growth lines, assuming the form of small, hardly visible rings toward the aperture. the tube widens before the aperture, forming a ring-like swelling, which is crossed by some illdefined annulations, after which it contracts again, ending with a very small ring. Microsculpture composed by a fine wormlike striation. Septum domeshaped, protruding, with a low dorsal mucro. Periostracum colourless. Operculum thin, flat, corneous, multispiral, internal side with a slightly raised nucleus sorrounded by a tight spire of 7 whorls, external side with a concave nucleus. Length: 1.9 mm.
Distribution: Caecum gulosum is found in the eastern Pacific Ocean (Pizzini et al. 2013). A single specimen tentatively attributed to this species was found on the eastern coast of South Africa (Fig. 13). the presence of Caecum gulosum in South Africa needs confirmation. Distribution: Caecum musorstomi occurs in the SW Pacific, Japan and Philippine Is. two specimens tentatively attributed to this species were found on the eastern coast (Fig. 13). the presence of C. musorstomi in South Africa needs confirmation.
Remarks: Two worn specimens on the whole fitting Caecum musorstomi were found on the eastern coast of South Africa. However, attribution to this species is only tentative as both annular sculpture and longitudinal microsculpture are not clearly visible.     Distribution: IndoWest Pacific; this species is very common on the eastern coast of South Africa (Fig. 15). Remarks: South African specimens show no relevant differences with respect to the specimens found all over the IndoWest Pacific.
Caecum lindae sp. n. Figs 15, 25K Etymology: Named after Linda Davis, collections manager for Mollusca at NMSA. Description: Tube subcylindrical, flaring towards the aperture. Aperture oblique, contracted, ending with three concentric rings. Septum protruding, with a strong, pointed mucro with subtriangular outline, slightly displaced toward the right side. Ventral side of the septum convex, dorsal one slightly concave. Early stages and operculum unknown. Length: 2.5 mm. type locality: SOUtH AFRICA: Eastern Cape: Agulhas Bank, off Cape Morgan Lighthouse, -100 m. Distribution: Currently known only from the type locality, Cape Morgan, north of East London (Fig. 15). Remarks: Caecum lindae sp. n. shows a unique shape of the septum among South African species. It can only be compared with C. geigeri Pizzini & Raines, 2011, described from Austral Is., due to the similar shape of the septum, but it can be distinguished by the different shape of the tube and by the absence of the strong annulations preceding the aperture.
Distribution: Caecum oahuense is found in the eastern Pacific Ocean (Pizzini & Raines 2011). A single specimen tentatively attributed to this species was found on the eastern South African coast (Fig. 15). the occurrence of Caecum oahuense in South Africa needs confirmation.
Distribution: IndoWest Pacific; in South Africa this species was collected from the eastern coast (Fig. 17). Remarks: this species is characterized by the presence of some rings in the abapical portion of the tube and by a low dome-shaped septum without mucro.   this species as common at Port Alfred. We found only a few specimens in the rich material stored in the NMSA. South African specimens fit well with C. glabrum as commonly intended and only minor differences can be accounted for, such as a shorter and proportionally wider tube, a more pronounced swelling at the aperture and a duller surface. Notwithstanding these minor differences, the identification of South African specimens as C. glabrum is problematic. In fact, both present and historical records of this species in South Africa, ignoring possible misidentifications, come from the central and eastern part of the southern coast of South Africa, and there is no information about its occurrence either in the western part of the southern coast or along the western coast of Africa from Guinea to western South Africa.
With the present knowledge coming from studies on other groups, it seems unlikely to find species with a continuous distribution going from western Africa to southern South Africa. Among other well-studied molluscan families, there are only a few species with a western African or European to southern South African distribution, e.g. Talochlamys multistriata (Poli, 1795) among Pectinidae, which nevertheless shows a gap in Namibia (Dijkstra & Kilburn 2001). Furthermore, the pattern of southeastern Atlantic currents, with a northwardflowing Benguela Current and a southwardflowing Angola Current, which meet at around the Angolan-Namibian border, strongly suggests that western African and South African species are unrelated. However, the identity of European and South African populations cannot be ruled out, as it has been genetically demonstrated with a species of spider crab from the Lusitan area and South Africa (Sotelo et al. 2009).
For the time being, in the absence of a detailed study of European C. glabrum and more information coming from South African populations, we ascribe South African specimens to the European species by comparison only.  de Folin, 1868 (■), C. succineum de Folin, 1880 (▲) and C. cf. glabrum (Montagu, 1803) (▼).

Subfamily Pedumicrinae Iredale & Laseron, 1957
Genus Parastrophia de Folin, 1869 type species: Moreletia cornucopiae de Folin, 1869(by original designation, Folin 1869 from Pacific Ocean. 20, 25B, C Etymology: Derived from the Latin adjective ornatus (= adorned), referring to the longitudinal microsculpture that adorns the teleoconch. Description: tube bisinuous, semitransparent, vitreous. Coiled protoconch formed by about 1.1 whorls; uncoiled protoconch conical, about 0.5 mm long, ending in a clear varix. The varix is asymmetrical, flangelike in the adapical side, shaped into a ring in the abapical side. teleoconch smooth, with only some growth lines, especially close to the aperture, defining irregular rings. Microsculpture composed by fine longitudinal threads, slightly dextrally wound around the tube, rather sparse adapically, finer and denser abapically. the threads are interrupted by the growth lines, producing a wavy appearance. Operculum unknown. Length: 2.5-2.7 mm. type locality: SOUtH AFRICA: Eastern Cape: Mzamba. Distribution: Eastern coast of South Africa (Fig. 20). Remarks: this species can be compared with the Australian Parastrophia cygnicollis (Hedley, 1904) and P. erseusi Hughes, 1993. It differs from the former by the different shape of the tube, which is longer and more slender in P. cygnicollis, by the shape of the adapical side of the varix, smoothly flaring in cygnicollis, flangelike in ornata, and by the presence of a microsculpture composed of fine longitudinal threads, whereas in cygnicollis a microsculpture composed of a few longitudinal wavy grooves is sometimes visible (Pizzini et al. 2013: fig. 16O). Conversely, Parastrophia erseusi differs by the more or less symmetrical, evenly rounded varix and by the absence of microsculpture (Hughes 1993). Parastrophia ornata sp. n. is also similar to P. melanesiana Pizzini, Raines & Vannozzi, 2013, which shares a similar microsculpture, but differs from it by the paucispiral coiled protoconch and by the different shape of the separation varix. 20, 25A Etymology: The name is composed by the Greek α (not) and the Latin adjective varicosus (= provided with a varix) due to the absence of the varix between the uncoiled protoconch and the teleoconch that occurs in all the other Parastrophia species. Description: tube slightly bisinuous, very thin, vitreous, tapered. Coiled protoconch small, ovoid, of half a whorl. Uncoiled protoconch smooth, conical in the adapical half, then subcylindrical, curved and with a slight constriction before the transition to the teleoconch, which is marked by a simple scar. teleoconch gently curved and slowly growing, characterized by the presence of a microsculpture composed by shallow, irregularly set grooves spaced about 5 µm apart. Aperture rounded, simple, without any feature. Length 1.5 mm. Operculum unknown. Comparative material examined: P. cornucopiae de Folin, 1869, lectotype (MNHN-IM-2000 selected by Pizzini et al. 2013Pizzini et al. (2013 fig. 16F, G); P. filum Melvill, 1906, holotype from Gulf of Oman, 156 fms (NHMUK 190610.23.47); P. japonica Hinoide & Habe, 1978, holotype (NSMt-Mo 55474); P. melanesiana Pizzini, Raines & Vannozzi, 2013, holotype (MNHN-IM-2000. Distribution: this species is known only from the eastern coast of South Africa (type locality, Fig. 20) and from the southern coast of Madagascar around talanaro. Remarks: Parastrophia avaricosa sp. n. is the only known Parastrophia species without a separation varix between protoconch and teleoconch, thus it is immediately distinguished from all the other congeners. the new species resembles P. cornucopiae de Folin, 1869, P. japonica Hinoide & Habe, 1978and P. melanesiana Pizzini, Raines & Vannozzi, 2013(all figured in Pizzini et al. 2013 due to the paucispiral protoconch. Parastrophia cornucopiae is similar to P. avaricosa, having in common a similar shape of the protoconch, but the latter completely lacks the varix separating the uncoiled protoconch from teleoconch. Moreover, Parastrophia avaricosa shows a microsculpture composed by fine collabral grooves that is not observed in P. cornucopiae. Parastrophia avaricosa is also similar to P. japonica and P. melanesiana, but the latter two show a distinct separation varix and a longitudinal microsculpture (Pizzini et al. 2013).

DISCUSSION AND CONCLUSIONS
South African Caecidae are revealed to be unexpectedly diverse. In fact, while historical accounts mentioned only two species, South African caecid fauna turned out to be much richer, with 20 recognized species, of which 18 belong to the genus Caecum and two to the genus Parastrophia.
Regarding Caecum species, larval stages could not be attributed with certainty. two types of larval shells were found in the samples coming from the warm temperate south coast. Both show a multispiral protoconch and an attached tube without sculpture and microsculpture, and could be likely attributed to either C. austrafricanum sp. n. or C. intortum sp. n. they differ only in the diameter of both the protoconch and the attached tube. As the smaller type is more abundant and occurs also where C. intortum was not found, it may be hypothesized that it belongs to C. austrafricanum, while the larger type could belong to C. intortum.
Caecum austrafricanum sp. n., C. knysnaense sp. n. and C. intortum sp. n. form a complex of species that share several morphological characters, such as the whitish and semitransparent tube without sculpture or microsculpture, the large macula with a frosted appearance and the mucronate septum. Within a common range of distribution, they are found in sympatry and may at first sight be confused with one another. However, they show some constant characters that allow an unambiguous specimen determination. these three species are also probably related to both C. macrum van der Linden & Moolenbeek, 2000 and Caecum crassum de Folin, 1870 from western Africa. At least five out of the 20 Caecidae species recorded from South Africa show a ventral spot here referred to as macula (table 1). two distinct morphologies have so far been observed: a) large and with a frosted appearance in Caecum austrafricanum sp. n., C. knysnaense sp. n. and C. intortum sp. n., and b) small and whitish or colourless in C. leilae sp. n. and C. inhacaense Albano & Pizzini, 2011, respectively (Fig. 24A-G). the macula is visible in fresh, adult specimens and is located in the middle of the ventral side of the tube, more or less displaced toward the left side. the macula lies in the region of the tube where the columellar muscle is connected to the shell (Götze 1938). In a photograph of a living C. glabella auct. non Adams, 1868 withdrawn inside the tube reported by Sasaki (2006: fig. 4), a kidneyshaped feature can be seen through the transparency. In correspondence with this, in the lateral view the tube appears to be opaque, possibly due to the formation of a callus where the muscle is connected to the shell. As SEM investigation revealed no difference in surface morphology with respect to other regions of the shell, it is likely that this spot is due to muscular impression as seen through the transparency. Outside South Africa, the macula was detected in the western African C. macrum van der Linden & Moolenbeek, 2000 and Caecum crassum de Folin, 1870 (Fig. 24H, I). It is possible that this character occurs in several other Caecum species and may have been overlooked by past authors since caecids are normally shown in lateral rather than in ventral view. Moreover, the periostracum can also mask the presence of the macula. Within the limits of the species treated in the present revision, the shape of the macula seems to be speciesspecific and may be used as an additional character for species identification. In fact, in species where the macula occurs, only rarely could it not be observed in adult, fresh specimens.
Some Caecum species show a more or less marked dextral torsion of the tube. In C. intortum sp. n. it is evident and causes the aperture to be clearly inclined toward the  fig. 2E). We do not agree with Lightfoot (1992), who stated that torsion of the tube is not a reliable character. In fact, torsion of the tube has been observed in other species such as C. dakuwaka Pizzini, Raines & Vannozzi, 2013, and in our opinion can be considered a useful diagnostic character. the septum of some species, such as Caecum incisum sp. n., C. maraisi sp. n. and C. leilae sp. n., shows some oblique, roughly parallel scars resembling concentric waves originating from the mucro. This feature was first reported by van der Linden & Moolenbeek (2000) for Caecum vicinum de Folin, 1870 and later observed in other species such as C. inflatum de Folin, 1869, C. maestratii Pizzini, Raines & Vannozzi, 2013and Meioceras kajiyamai Habe, 1963(Pizzini et al. 2013. the origin of these scars is unknown and they may possibly be regarded as growth lines of the septum. South African coasts show a wide variety of climates, ranging from the cold temperate west coast, the warm temperate south coast and the subtropical and tropical east coast (teske et al. 2011). these diverse climates are mainly determined by the interplay of two major oceanic currents, namely the Agulhas Current, flowing southward along the eastern coast of South Africa and bringing warm water from the Indian Ocean, and the cold Benguela Current, which flows northward along the western South African and Namibian coasts. Because of its geographical position, and the influence of the Agulhas-Benguela system, South Africa acts as a watershed between the Atlantic and Indian oceans, which can be considered to be well-separated biomes (teske et al. 2011). the high marine biodiversity of South Africa is accounted for in recent papers (turpie et al. 2000;Griffiths et al. 2008). the pattern of Caecidae biodiversity follows a west-east gradient, in agreement with the literature (turpie et al. 2000). In fact on the east coast,  With the present knowledge, half of the Caecidae species occurring in South Africa can be considered endemic. Most are distributed in the southern, warm temperate to subtropical region (Caecum austrafricanum, C. incisum, C. intortum, C. knysnaense, C. lindae, C. maraisi, C. morgan and C. subquadratum), while only two occur in the subtropical/tropical region (C. leilae and Parastrophia ornata). the remainder are represented by species either occurring in the southwestern Indian Ocean (Caecum inhacaense and Parastrophia avaricosa) or that have a wide Indo-West Pacific distribution (Caecum chinense, C. neocaledonicum, C. sepimentum and C. succineum). the presence of Caecum glabrum, C. gulosum, C. musorstomi and C. oahuense in South Africa needs confirmation.