Vaceuchelus jayorum, 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 : 455-457

Vaceuchelus jayorum sp. n.

Figs 45 , 46 , 49

Etymology: Named for Maurice and Danielle Jay of Réunion, in recognition of their contribution to our knowledge of the Mascarene malacofauna, and in gratitude for the hospitality they afforded the author.

Description:

Shell: Small, turbiniform (L/D=1.00–1.16); teleoconch of up to 3.5 whorls; sculpture strongly cancellate; first whorl initially sculptured only by axial pliculae, relatively widely spaced at first, but becoming more close-set toward end of first half whorl; 3 spiral cords develop during first whorl, one at mid-whorl, one between this and adapical suture and the third level with abapical suture; that at mid-whorl strongest and becoming peripheral cord of later whorls; cords become progressively stronger with growth, a fourth appearing below adapical suture during third whorl; axial pliculae more widely and regularly spaced from second whorl onward; pliculae cross cords producing angular nodules at intersections; in final quarter of last adult whorl an additional intermediary spiral cord arises between each of the primary cords ( Fig. 45F ); for the most part, intervals between cords noticeably wider than cords themselves; last adult whorl with 25–30 pliculae; pliculae narrower than cords; interstices obliquely quadrate. Base with 4 somewhat more close-set spiral cords, including that level with suture, a weaker fifth one sometimes evident, closely juxtaposed to the fourth and spiralling into umbilicus; umbilicus remaining patent at maturity, its width variable between individuals, often somewhat obscured by reflected upper part of columella lip. Peristome markedly oblique, almost tangential; aperture subcircular; columella concave, lacking dentition; outer lip notched at ends of spiral cords, somewhat thickened internally, but lacking both internal teeth and in-running ridges; interior of aperture nacreous, angled beneath external cords.

Microsculpture ( Fig. 46B, C ): Vermiform spiral threads not evident on apical whorls; microsculpture between axial pliculae crisply granular; this persisting over much of adult shell, but traces of scratch-like sculpture evident in interstices; in fresh specimens microsculpture generally obscured by relatively thick intritacalx layer and additional superficial encrustations.

Protoconch ( Fig. 46A, C ): White, not exsert, slightly down-tilted and more or less level with first teleoconch whorl; diameter 260–290 μm; terminal lip straight but with evidence of a small beak-like projection near adapical suture; superficial sculpture well developed, relatively coarse and widely spaced, arranged in irregular axial lines, with no spiral component evident.

Colour: Shell more or less uniformly white to pale buff; with a dirty white, chalky intritacalx deposit.

Dimensions: Largest specimen, length 2.9 mm, diameter 2.5 mm.

Operculum: Like that of V. natalensis .

Radula and external anatomy: Unknown.

Holotype ( Fig. 45A–C ): RÉUNION: not further localised (M. Jay coll’n, MNHN 24809 ).

Paratypes: RÉUNION: Cap la Houssaye (21.01797°S 55.23709°E), - 12 m, hand-dredged sand, J. Drivas, 1987 ( NMSA K2755 /T2959, 3 specimens) ; not further localised (M. Jay coll’n, MNHN 24810 , 35 specimens; NMSA L8467/T2960, 4 specimens; NHMUK 20110385 , 1 specimen) . MADAGASCAR: Andramara (25.48000°S 44.97167°E), intertidal roche basaltique, dalles sableuses, Exped’n ATIMO VATAE, st’n BM10, 2.vi.2010 ( MNHN 24811 , 2 specimens) .

Other material examined: RÉUNION:not further localised (M. Jay coll’n, MNHN) . RODRIGUES: Between Anse aux Anglais and Pointe Venus (19.6752°S 63.4313°E), beach-drift, D. Herbert, ix.1991 ( NMSA K7825 ) ; Grand Baie , near stream (19.67175°S 63.45089°E), beach-drift, D. Herbert, ix.1991 ( NMSA L549 ) . MOZAMBIQUE: Inhambane area, off Ponta da Barra lighthouse, ‘ Stalin Reef’ (23.68798°S 35.52566°E), - 16 m, dived D. Slater, xi.2003 (D. Slater coll’n) .

Distribution and habitat ( Fig. 49 ): Endemic to the tropical south-western Indian Ocean, ranging from the Mascarene Islands, particularly Réunion, to southern Madagascar and central Mozambique. No accurate habitat data available, but probably an inhabitant of near-shore, carbonate substrata and perhaps lagoons.

Remarks:This material is confusingly similar to specimens of V. natalensis from off-shore habitats, in which the axial pliculae cross the spiral cords to produce a more angularly nodular sculpture. The principle discriminant character of the present material is the appearance of intermediary spiral cords above the periphery of the final quarter of the last adult whorl. Such intermediary cords are never evident in V. natalensis . In addition, the axial pliculae on the first teleoconch whorl are considerably more close-set in V. jayorum and the intritacalx deposit is more uniformly pale in colour, lacking the greyish axial banding common in V. natalensis .

There is also some resemblance to V. favosus (Melvill & Standen, 1896) , a poorly known species from the Loyalty Islands. However, the figured syntype of that species (MMUM EE.3734; here re-illustrated and designated lectotype, Fig. 70E–G ) also lacks intermediary spiral cords in the final quarter of the last adult whorl, and it has a wider umbilicus than any of the south-western Indian Ocean species of Vaceuchelus .

Figures

Fig. 45. Vaceuchelus jayorum sp. n.: (A–C) holotype, diameter 2.5 mm (M. Jay coll’n, MNHN 24809); (D) depressed specimen, Réunion, diameter 2.4 mm (paratype, M. Jay coll’n, MNHN 24810); (E) Andramara, southern Madagascar, diameter 2.4 mm (paratype,MNHN 24811); (F) side view showing intermediary spiral cords on final partof last adult whorl,SEM,Réunion,diameter 2.35 mm (paratype, M. Jay coll’n, MNHN 24810).

Fig. 46. Vaceuchelus jayorum sp. n., Réunion (paratypes, M. Jay coll’n, MNHN 24810): (A) apical whorls showing strong,close-set, axial pliculae on first whorl, bar = 0.5 mm;(B) adult microsculpture, bar = 250 µm; (C) protoconch, bar = 200 µm.

Fig.49.Distribution of Vaceuchelus jayorum (triangles) and V.natalensis (squares).Each symbol represents one or more records.

Fig.70.Vaceuchelus species examined for comparison:(A, B) Euchelus cavernosus Sowerby, 1905, one of three syntypes, specimen marked with an X, Sri Lanka, length 7.2 mm, diameter 7.0 mm (NHMUK 1905.10.23.6–8); (C, D) Monodonta clathrata A. Adams, 1853, one of three syntypes, Bohol, Philippines, length 9.3 mm, diameter 7.8 mm (NHMUK 196868); (E–G) Euchelus favosus Melvill & Standen, 1896, figured syntype (here designated as lectotype) length 2.63 mm, diameter 2.60 mm (MMUM EE.3734, McGhie 2008). Not to scale, E–G enlarged relative to A–D.