Vaceuchelus natalensis (Smith, 1906)
Herbert, D. G., 2012, A revision of the Chilodontidae (Gastropoda: Vetigastropoda: Seguenzioidea) of southern Africa and the south-western Indian Ocean, African Invertebrates 53 (2), pp. 381-381 : 457-461
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|Vaceuchelus natalensis (Smith, 1906)|
Euchelus natalensis : Smith 1906: 55, pl. 8, fig. 5; Barnard 1963: 266 (in part). Type loc.: Durban, South Africa [H.C. Burnup].
Shell: Small, turbiniform; spire height rather variable (L/D=0.90–1.2); teleoconch of up to 3.5 whorls; sculpture strongly cancellate; first whorl initially sculptured only by relatively widely spaced axial pliculae (16–18), but 3 spiral cords develop soon thereafter, one forming shoulder, another level with abapical suture and the third between these, at whorl periphery; cords persist and become progressively stronger with growth; a fourth cord may develop on shoulder during last or penultimate whorl, but otherwise there are no intermediaries; intervals between cords noticeably wider than cords themselves; cords sometimes weakly and rather irregularly granular where crossed by axial pliculae (see notes below); last adult whorl with 22–30 pliculae; pliculae narrower than cords; interstices obliquely quadrate. Base with 4 somewhat more close-set spiral cords, including that level with suture, with a weaker fifth one spiralling into umbilicus; umbilicus narrowly patent, partly obscured by reflected columella lip. Peristome oblique; aperture subcircular; columella concave, lacking dentition; outer lip strongly notched at ends of spiral cords, even in the largest specimens; interior of aperture nacreous, lacking internal teeth or spiral ridges, but angled beneath external cords.
Microsculpture ( Fig. 48B, C View Fig ): Vermiform spiral threads not evident on apical whorls, but traces of microscopic granular sculpture present; scratch-like microsculpture weakly evident in sculptural interstices of adult shell, but microsculpture generally obscured by granular intritacalx deposit.
Protoconch ( Fig. 48A, C View Fig ): White, a little exsert and slightly down-tilted; diameter 280–300 μm; lacking an apical beak; terminal lip more or less straight to weakly convex, and slightly flaring; superficial sculpture well developed, arranged in irregular axial lines, with no spiral element evident.
Colour: Shell whitish, living specimens with a dirty buff intritacalx deposit, usually with darker, ashy-grey axial bands, some iridescence in cord intervals; dead shells usually with only traces of intritacalx remaining, mostly in interstices.
Dimensions: Largest specimen, length 3.3 mm, diameter 3.4 mm.
Operculum ( Fig. 4K View Fig ): Relatively tightly multispiral throughout.
Radula ( Fig. 48D, E View Fig ): Formula ∞+2+1+2+∞; ca 60 transverse rows of teeth; transition from lateral to marginal series relatively clear. Rachidian with large trigonal cusp and well-developed hood; cusp with very strong transverse ridge at its base; cutting edge coarsely dentate, central denticle largest, lanceolate, with approx. 4 smaller denticles on each side. Only 2 lateral teeth evident, their cusps spathulate with coarsely and deeply dentate margins. Marginals resembling those of Herpetopoma , the inner ones with cusp coarsely pectinate on outer margin; remaining marginals with smaller more finely pectinate cusps, but those at radula margin broader and flatter.
External anatomy ( Fig. 6G View Fig ): Head-foot translucent milky-white when alive, snout and neck with some greyish pigmentation. Cephalic lappets present but small and not extending across forehead; right postocular peduncle well developed, similar in size to eyestalk or perhaps larger; right subocular tentacle not evident; neck lobes similar, each with 5 or 6 tentacles of varying size; epipodium posterior to neck lobes with 4 or
5 tentacles of varying sizes on each side, with an epipodial sense organ faintly discernable at base of larger ones.
Type material: Lectotype (here designated, Fig. 47A–C View Fig ) of Euchelus natalensis Smith, 1906 , in NMSA (1208/T522), length 2.8 mm, diameter 2.9 mm; also three paralectotypes ( NMSA W7531 View Materials /T2642); three further paralectotypes in NHMUK (1906.6.23.18–20). All are fresh specimens, but none is obviously the one originally figured.
Additional material examined (all NMSA unless indicated otherwise): MOZAMBIQUE: Bazaruto Archipelago , Santa Carolina Is. (21.6124°S 35.3399°E), R. Kilburn, ix.1974 (K3929) GoogleMaps ; ditto, south sandbank (21.6124°S 35.3399°E), R. Kilburn, 17.viii.1974 (K1991) GoogleMaps ; Malongane , coral reef 5 km north Ponta do Ouro (26.7983°S 32.8906°E), - 15–20 m, hand-dredged sand, D. Herbert, v.1994 (L1653) GoogleMaps . SOUTH AFRICA: KwaZulu-Natal: Kosi Bay , main reef 1–2 km south of estuary (26.9083°S 32.8861°E); - 9–17 m, sorted from stone washings, D. Herbert, 12–20.vii.1987 (D9827) GoogleMaps ; ditto, main reef, 1–4 km south of estuary mouth (26.9210°S 32.8861°E), living, - 20 m, underwater pump, D. Herbert & R. Broker, 5.v.1990 (S2524) GoogleMaps ; ditto, living, - 15 m, stone surfaces, D. Herbert, 4.v.1990 (S2880) GoogleMaps ; off Kosi mouth (26.9333°S 32.9117°E), - 50 m, fine sand, shell rubble, Codium , dredged NMDP, RV Meiring Naude, st’n ZA2, 6.vi.1987 (E1468) GoogleMaps ; between Bhanga Neck and Kosi Bay , reef off marker 13 north near pinnacles (26.93°S 32.90°E), - 10–12 m, hand-dredged sand, D. Herbert, 12.v.1990 (S2482, S3106) GoogleMaps ; ditto, - 8 m, underwater pump, D. Herbert & K. Bloem, 6.v.1990 (S2769) GoogleMaps ; off Dog Point (27.1083°S 32.8817°E), - 70 m, sandstone conglomerate, dredged NMDP, RV Meiring Naude, st’n ZC3, 4.vi.1987 (E1736) GoogleMaps ; off Lala Neck (27.2250°S 32.8250°E), - 74 m, shells and sand, dredged NMDP, RV Sardinops , st’n ZDD3, 8.vi.1990 (S9768) GoogleMaps ; Sodwana Bay, 2– Mile Reef (27.517°S 32.700°E), - 10–15 m, sorted from stone washings, D. Herbert & R. Broker, ix.1987 (E740) GoogleMaps ; ditto, - 10–15 m, hand-dredged sand, D. Herbert, 30 xii.1990 (S4311) GoogleMaps ; ditto, outer edge of reef, - 15–17 m, sorted from stone-washings, D. Herbert, 18–26 x.1986 (D5298) GoogleMaps ; Leadsman Shoal , outer portion (27.80°S 32.62°E), - 24–26 m, sorted from stone washings, D. Herbert & NPB, 14.v.1988 (E2673) GoogleMaps ; Leadsman Shoal, Raggie Reef, 1–2 km north of Leven Point (27.80°S 32.62°E), living, - 8–12 m, mixed algal & coral reef, D. Herbert & NPB, 15.v.1988 (E6809) GoogleMaps ; NE of Leven Point (27.9167°S 32.6467°E), - 250 m, coarse sand, dredged NMDP, RV Meiring Naude, st’n ZL5, 9.vi.1988 (S1140) GoogleMaps ; off Leven Point (27.9250°S 32.6083°E), - 50–60 m, mud, dredged NMDP, RV Meiring Naude, st’n ZL1, 9.vi.1988 (E5873) GoogleMaps ; Umdloti (29.6829°S 31.1127°E), intertidal, under rocks, ix.1974 (J. Marais coll’n 281) GoogleMaps ; Durban (29.850°S 31.017°E), H.C. Burnup (A4564); Durban Bay (29.850°S 31.017°E), shallow dredgings, B.J. Young (E599); Umkomaas (30.2064°S 30.8023°E), living, H.C. Burnup (A4563); Widenham , intertidal rocks (30.216829°S 30.798644°E), low shore spring tide, under large rocks with spaces below, together with arcid and carditid bivalves, leg. D. Herbert & L. Davis, 23.ix.2010 (W7462) GoogleMaps ; Aliwal Shoal (30.2833°S 30.8333°E), D. Herbert & R. Emanuel, 27 xi.1988 (E6189) GoogleMaps ; ditto, - 10 m, sand & reef debris, hand-dredged, D. Herbert, 4.iv.1992 (S8222) GoogleMaps ; ditto, - 10–20 m, hand-dredged sand, D. Herbert, 30.vi.1991 (S8021) GoogleMaps ; ditto, - 14 m, underwater pump, D. Herbert, 2.vi.1991 (S8673) GoogleMaps ; ditto, - 16 m, hand-dredged sand, D. Herbert, 26.v.1990 (S5993) GoogleMaps ; ditto, - 27 m, in silt from between rocks, G. Smith, don. J. Marais, iii.1988 (E1675, J. Marais coll’n 280) GoogleMaps ; ditto, Cracker Reef , ca - 23 m, D. Herbert, 30.iv.1989 (E7141) GoogleMaps ; Scottburgh (30.283°S 30.833°E), C.W.Alexander, ex W. Falcon coll’n (A4565); Landers Reef off Park Rynie (30.333°S 30.817°E), - 29–30 m, sorted from stone washings, D. Herbert, 2.v.1988 (E2251) GoogleMaps ; off Umzinto (30.36°S 30.85°E), living, - 84 m, dredged NMDP, RV Meiring Naude, st’n X2, 15.viii.1982 (D5428) GoogleMaps . Eastern Cape: Mbotyi (31.45°S 29.73°E), beach drift, R. Kilburn & D. Herbert, v–vi.1985 (C8468) GoogleMaps ; Lwandile / Mdumbi (31.883°S 29.267°E), R. Kilburn & R. Fregona, vii.1981 (C205) GoogleMaps ; Xora River mouth (32.1600°S 28.9974°E), R. Kilburn (7059); off Nthlonyane River (32.2133°S 28.9817°E), - 51 m, sandy mud with astrorhizid foraminiferans, dredged NMDP, RV Meiring Naude, st’n P7, 19.vi.1982 (E164) GoogleMaps ; Pondoland coast, Mrs A. Filmer , H. Becker coll’n, ex Transvaal Mus. 1978 (B1104) .
Distribution and habitat ( Fig. 49 View Fig ): Southern Mozambique (Bazaruto Archipelago) to just north of the Mbashe River, Eastern Cape, South Africa; from the low intertidal zone of rocky shores to - 84 m; in intertidal habitats specimens may be found living at LST under large rocks that are rarely moved by the waves and which have a space beneath them allowing water flow, usually together with arcid and carditid bivalves. I believe Turton’s record of the species from Port Alfred, Eastern Cape ( Turton 1932) was almost certainly based on material of V. gemmula , which Bartsch had earlier mistakenly identified as V. natalensis .
Remarks: There is noticeable intraspecific variation in the extent to which the axial pliculae interact with the spiral cords. In intertidal material the interaction is minimal and the spiral cords are smooth or at most irregularly undulant. This is the typical condition ( Fig. 47A–G View Fig ). Generally, in specimens from off-shore reefs, however, the axial pliculae are more close-set and they cross the spiral cords, rendering the latter distinctly nodular ( Fig. 47H, I View Fig ). Such specimens closely resemble V. jayorum from Réunion, but they do not develop intermediary spiral cords on the last adult whorl.The distinguishing features of V. gemmula have been detailed above.
V. cavernosus (Sowerby, 1905) View in CoL from Sri Lanka ( Fig. 70A, B View Fig ) and V. clathratus (A. Adams, 1853) from the Philippines ( Fig. 70C, D View Fig ) likewise lack apertural dentition, but are both considerably larger, whereas V. semilugubris View in CoL (below) although equally small, generally has blackish maculations and develops denticles inside the outer lip when mature.
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