Vaceuchelus gemmula ( Turton, 1932 ) Herbert, 2012

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 : 452-455

Vaceuchelus gemmula ( Turton, 1932) comb. n.

Figs 42–44

Euchelus gemmula: Turton 1932: 194 , No 1347, pl. 49. Type loc.: Port Alfred , South Africa.

Euchelus natalensis: Bartsch 1915: 163 ; Turton 1932: 193, No 1346; Barnard 1951: 117, pl. xvi, fig. 16;

1963: 266 (in part).

Etymology: The species name gemmula , diminutive of Latin gemma (a bud or jewel) was formed as a feminine noun in apposition.

Description:

Shell: Small, turbiniform (L/D=0.90–1.15); teleoconch of up to 3.5 whorls; sculpture strongly cancellate; first whorl initially sculptured only with widely spaced, rib-like, axial pliculae (ca 15), but 3 spiral cords develop soon thereafter, one forming shoulder, another level with the abapical suture and the third between these at whorl periphery; cords persist and become progressively stronger with growth; an additional (fourth) subsutural cord may or may not develop on the shoulder during the last or penultimate whorl; no intermediary spiral cords; intervals between cords wider than cords themselves; last adult whorl with 20–30 axial pliculae; pliculae narrower than cords and somewhat lamellate, sometimes raised into squamose nodules where they cross cords; interstices obliquely quadrate. Base with 3 spiral cords, including that level with suture, usually with a weaker, rather ill-defined, fourth one present adjacent to columella; umbilicus closed or at most chink-like in adult, more obviously patent in some juveniles. Peristome oblique, aperture subcircular; columella concave, lacking dentition; outer lip notched at ends of spiral cords in juveniles and subadults, but less so in the largest specimens, when growth has ceased; even in the most mature specimens the outer lip is not conspicuously thickened and there is no trace of apertural teeth; interior nacreous and smooth, save for weak angles beneath external cords.

Microsculpture ( Fig. 43B, C ): Vermiform spiral threads not evident on early whorls; later whorls with a granular microsculpture on the spiral ribs and sparse scratch-like marks in the sculptural interstices.

Protoconch ( Fig. 43A, C ): White, a little exsert and slightly down-tilted; diameter ca 340 μm; terminal lip very weakly convex; superficial sculpture well developed, arranged in irregular axial lines, spiral element weakly evident in some specimens.

Colour: White to pale greyish white, living specimens with dirty buff intritacalx deposit, particularly in sculptural interstices. Most material worn.

Dimensions: Largest specimen, length 4.2 mm, diameter 3.9 mm.

Operculum: Relatively tightly multispiral throughout.

Radula: Unknown.

External anatomy: Uniformly white and evidently chilodontid, but preservation of material inadequate to establish anatomical details.

Type material: The type lot at OXUM contains three specimens, one, the largest, is marked with an X in the aperture. It is here figured and designated lectotype ( Fig. 42A ). This is probably the originally figured specimen, but it is difficult to be certain since the original illustration was heavily retouched.

Additional material examined (all NMSA unless indicated otherwise): SOUTH AFRICA: Eastern Cape: off Mtamvuna River (31.1466°S 30.2666°E), living, - 115 m, sponge and rocks, dredged NMDP, RV Meiring Naude, st’n A13, viii.1981 (E858) ; ditto (31.1483°S 30.2617°E), - 111 m, sponge, dredged NMDP, RV Meiring Naude, st’n A14, 18.viii.1981 (E276) ; ditto (31.1500°S 30.2583°E), - 110 m, some pebbles, dredged NMDP, RV Meiring Naude, st’n A9, 18.viii.1981 (E6993) ; off Port Grosvenor (31.4166°S 29.9667°E), - 100–110 m, pebbles, some sand, dredged NMDP, RV Meiring Naude, st’n D6, 13.viii.1981 (E285) ; ditto (31.4166°S 29.9667°E), - 95–100 m, coarse sand, few gorgonians, dredged NMDP, RV Meiring Naude, st’n D12, 16.viii.1981 (E6981) ; ditto (31.40°S 29.95°E), - 80 m, calcareous coral nodules, lithothamnion sheets, dredged NMDP, RV Meiring Naude, st’n D20, 16.viii.1981 (S3174) ; ditto (31.3833°S 29.9333°E), - 60 m, sand and broken shell, dredged NMDP, RV Meiring Naude, st’n D22, 16.viii.1981 (E6979) ; ditto (31.4166°S 29.9333°E), - 82 m, worn coral nodules, dredged NMDP, RV Meiring Naude, st’n D18, 16.viii.1981 (E6980) ; ditto (31.4466°S 29.9333°E), - 97–100 m, sandstone, pink gorgonians, dredged NMDP, RV Meiring Naude, st’n D14, viii.1981 (C974) ; off N’tafufu River (31.5783°S 29.6617°E), - 50 m, mud and sand, dredged NMDP, RV Meiring Naude, st’n H6, 14.viii.1981 (E240) ; Mgazi River mouth (31.7283°S 29.5317°E), don. Mrs P. Palmer, viii.1980 (B3173) ; off Mbashe River (32.3567°S 29.0500°E), - 465–500 m, coarse sand, dredged NMDP, RV Meiring Naude, st’n Q13, 6.vii.1985 (C9372) ; off Shixini Point (32.5267°S 28.8833°E), - 500 m, muddy sand, coral rubble, dredged NMDP, RV Meiring Naude, st’n T17, 13.vii.1984 (V2786); off Qora River (32.5567°S 28.8000°E), - 100 m, coarse sand, some sponge rubble, dredged NMDP, RV Meiring Naude, st’n U6,14. vi.1983 (E8266, S2657) ; off Qolora River (32.7848°S 28.5862°E), - 340–350 m, coarse sand, broken shell, dredged NMDP, RV Meiring Naude, st’n Y11, 14.vii.1984 (E6997) ; East London, reef off Kwelera River (32.910°S 28.111°E), living, - 20 m, dived B. Hayes, v.1992 (S6100) ; East London (33.0166°S 27.9166°E), ex Albany Mus. 1980 (B6626); Port Alfred (33.6°S 26.9°E), don. W.H. Turton, ex Albany Mus. 1980 (B7351); ditto, E.K. Jordan, ex Transvaal Mus. 1978 (B3416); Cannon Rocks (eastern end of Algoa Bay ) (33.75°S 26.55°E), xii.1987 (E1539 and J. Marais coll’n 278) ; Port Elizabeth, Noordhoek (34.0405°S 25.6421°E), F. Graeve, ix.1985 (J. Marais coll’n 279) ; Port Elizabeth, Willows (34.0452°S 25.6070°E), living, under rocks ca low neap tide level, G. Carstens, 7.vi.1986 (D3493) . Western Cape: Still Bay (34.3833°S 21.4500°E), purch. ex Mrs. C.M. Connolly, i.1974 (A3199) [record requires confirmation].

Distribution and habitat ( Fig. 44 ): Eastern Cape, South Africa; from the border with KwaZulu-Natal, south and west to the Port Elizabeth area; empty shells from beach drift to - 500 m; living intertidally (under rocks), or subtidally on firm substrata to - 115 m. A single isolated record from 400 km further to the west at Still Bay (Western Cape) requires confirmation.

Remarks: This species closely resembles Vaceuchelus natalensis and was in fact treated as a synonym thereof by Barnard (1963). There are, nonetheless, clear and consistent differences evident in adult individuals which indicate that two distinct taxa are involved. The most obvious of these are the larger protoconch, closed umbilicus and presence of only three major cords on the base in V. gemmula . In addition, the spiral cords of V. natalensis remain strong at the aperture margin, producing strong notches in the outer lip even in the largest individuals. Juvenile stages can be difficult to separate since the umbilicus of V. gemmula sometimes only closes in the later stages of growth. Turton (1932) observed that the axial pliculae were more numerous in V. gemmula (about 30 on last adult whorl) than in V. natalensis (ca 20). I cannot confirm this observation and find considerable overlap between the taxa in terms of the number of axial pliculae, as well as considerable intraspecific variation. The three specimens in the OXUM type lot have 20, 22 and 24 pliculae on the last adult whorl, the latter figure being that of the lectotype. V. gemmula evidently attains a somewhat larger size than V. natalensis .

Little material of this species is available and most is in poor condition; only one live-collected adult specimen was to hand. The largest examples were obtained from beach-drift, but these are generally badly worn. Specimens from deeper water, off-shore habitats tend to be somewhat smaller, evincing an adult labrum at diameter ca 3.0 mm, and as in V. natalensis (below) they exhibit stronger nodules where the axial pliculae cross the spiral cords. The larger, less nodular form, which lives on near-shore reefs and washes ashore, is the typical form.

Figures

Fig. 42. Vaceuchelus gemmula (Turton, 1932): (A) lectotype of Euchelus gemmula Turton, 1932, diameter 3.7 mm (OXUM); (B, C) live collected specimen, off Kwelera River, East London, South Africa, diameter 3.8 mm (NMSA S6100).

Fig. 43. Vaceuchelus gemmula (Turton, 1932), off N’tafufu River, Eastern Cape (NMSA E240): (A) apical whorls showing widely spaced axial pliculae on first whorl, bar = 250 µm; (B) adult microsculpture, bar = 200 µm; (C) protoconch, bar = 200 µm.

Fig. 44. Distribution of Vaceuchelus gemmula. Each triangle represents one or more records.