Ascetostoma providentiae ( Melvill, 1909 ) 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 : 420-425

Ascetostoma providentiae ( Melvill, 1909) comb. n.

Figs 4F , 5A , 6A , 18–20

Euchelus providentiae: Melvill 1909: 78 , pl. 5, fig. 1; Viader 1937: 56; Kaicher 1990: No 5709. Type loc.: Providence Is. ( Seychelles group), north east of Madagascar.

not Clanculus providentiae: Kosuge & Chino 1998: 79 , pl. 26, fig. 1.

Description:

Shell: Trochoid-turbiniform, moderately elevated (L/D=1.04–1.26); teleoconch of 5.0–5.5 rounded whorls; suture indented and somewhat channelled, that between last adult whorl and penultimate whorl inserted at level of second subperipheral cord, but descending below this just prior to aperture; exterior of outer lip with a broad low subterminal thickening. First teleoconch whorl with approx. 20 axial pliculae; 3 spiral cords develop during second whorl (lowest level with abapical suture), and a fourth arising beneath adapical suture near end of whorl; subsequent whorls with further cords arising through intercalation; penultimate whorl with 7–9 cords, sometimes alternating a little in strength, sometimes not; seventh cord usually peripheral; cords well defined, equal to or wider than their intervals. Axial pliculae of first whorl persist on later whorls rendering spiral cords beaded where they cross them; beads of early whorls more or less rounded, but later becoming somewhat axially elongate, those on subsutural cord usually largest; axial pliculae well developed on spire whorls rendering sculpture cancellate, usually less prominent on last adult whorl. Base with 6–7 primary spiral cords and occasional intermediaries, sculptured as above. Peristome markedly oblique, more or less in one tangential plane; aperture subcircular to D-shaped, flattened parietally; columella lip protrudes into aperture as a thickened pillar which bears 2 well-developed teeth separated by a concavity; basal tooth often squarish, upper one somewhat smaller and more rounded; a deep U-shaped notch separates basal tooth from first denticle of basal lip; parietal region with glossy, translucent inductural callus, sculptured with a variable number of ridges extending into aperture; ridges sometimes bifid terminally; a well-developed parietal tooth projects from paries over umbilical depression; umbilicus present, lined and apically plugged with smooth, white callus when mature, conventionally patent in juveniles; umbilical margin thickened, also covered with callus and bearing ridge-like denticles (only in fully mature of specimens); callus slightly raised basally and confluent with flaring margin of outer lip; interior of outer lip with 2 rows of ridge-like denticles (at maximal maturity), the inner row stronger and lying on subterminal thickening of lip interior, the outer row (on non-nacreous flaring lip margin) weaker and less distinct; 2 denticles of inner row, nearest basal columella notch, usually larger; a small rounded or elongate granule may be present on columella near bottom of basal columella notch; interior of aperture nacreous, somewhat angled beneath spiral cords of shell exterior, but not spirally lirate.

Microsculpture ( Fig. 19B, C ): Early teleoconch whorls with fine vermiform spiral threads; microsculpture of subsequent whorls often completely obscured by encrusting organisms; little evidence of any superficial intritacalx deposit and scratch-like sculpture scarcely evident; microsculpture instead comprising irregular, somewhat oblique, vermiform threads, most noticeable on the spiral cords ( Fig. 19B ).

Protoconch ( Fig. 19C ): Translucent white, peripherally tinged with orange; diameter ca 240 µm; somewhat globose and protruding slightly above first teleoconch whorl; sculptured with 3 fine, widely spaced, spiral threads, between which lie numerous, fine, close-set, oblique, axial threads; terminal lip with a well-developed angular projection just above mid-whorl.

Colour: Most specimens uniformly rich orange-brown with darker spots on spiral cords of second and third whorls; occasional specimens with alternating darker and lighter blotches below suture; cord intervals faintly iridescent; umbilical region white; pigmentation of old, dead shells frequently rather more pinkish/purplish brown. Shell exterior of live-taken specimens usually more or less entirely covered with a thin, brownish or blackish, spiculiferous, encrusting sponge ( Fig. 18E ).

Dimensions: Greatest length 9.0 mm, greatest diameter 8.0 mm, but size at maturity evidently variable; some specimens of length ca 7.0 mm possess mature apertural dentition.

Operculum ( Fig. 4F ): Initially tightly multispiral, but whorls broadening with growth and becoming more openly multispiral.

Radula ( Fig. 19D, E ): Formula ∞+4+1+4+∞; ca 75 transverse rows of teeth. Rachidian with trigonal cusp and well-developed hood; base of cusp with weak transverse ridge; cutting edge coarsely dentate, central denticle largest, lanceolate and with 3 or 4 smaller denticles on each side. Lateral tooth cusps with an elongate, rather spathulate central denticle and relatively coarse secondary denticles on outer margin, inner margin with few if any denticles. Inner marginals more slender with a recurved, dentate cusp, the denticles on outer margin extending some way down shaft; middle marginals very slen- der, but outermost ones shorter, broader and very delicate.

External anatomy ( Figs 5A , 6A ): Head-foot with extensive dark brown to black pigmentation in living animal; cephalic tentacles more or less uniformly dark; blackish colour of neck lobes and epipodial tentacles contrasting with whitish upper parts of foot. Cephalic lappets finely digitate, not meeting in mid-line; snout laterally expanded,

transversely striped with black, lips split mid-ventrally; right post-ocular peduncle relatively small, arising from base of eyestalk; subocular tentacle not evident; right neck lobe with approx. 5 closely spaced tentacles anteriorly (increasing in size from first to last) followed by 2 or 3 more widely spaced ones; left neck lobe with numerous, close-set tentacles along most of its length, more or less similar in size; epipodial fold with approx. 10 tentacles of various sizes, the larger ones each with a basal epipodial sense organ; epipodial sense organs not evident beneath neck lobes, but some larger neck lobe tentacles with a pale basal spot that may represent such a structure.

Type material: Melvill (1909) stated that he had examined two specimens and selected the larger as the ‘type’ [holotype]. The second specimen would therefore be a paratype. Two specimens were originally registered under NHMUK 1910.3.17.2–3, but only one is now present. This is smaller than the dimensions given by Melvill and is presumably the paratype; length 6.6 mm, diameter 5.9 mm. It is a subadult specimen in which the apertural dentition is not fully developed ( Fig. 18G, H ).

Additional material examined (all NMSA unless indicated otherwise): MADAGASCAR: W Banc du Leven (12.5333°S 47.6675°E), - 35–150 m, BENTHEDI Exped’n, st’n 5, dredged ( MNHN); west of Nosy Be (13.417°S 47.950°E), - 71–158 m, Campagne Miriky, st’n DW3230, dredged, 03.vii.2009 ( MNHN) . RÉUNION: off Étang-Salé-les-Bains, Marion-Dufresne 32, st’n DC176 (21.3333°S 55.1833°E), - 165–195 m, dredged, 1982 ( MNHN) . MOZAMBIQUE: Sofala Bank (approx. 20.123°S 35.543°E), - 110–145 m, ex pisce, v.2007 (J. Rosado coll’n) ; between Beira and Bazaruto (approx. 20.58°S 35.73°E), - 95–125 m, ex pisce (J. Rosado coll’n); off Lacerda Lighthouse (25.56167°S 32.84472°E), - 72–75 m, dredged, vii.2008 (J. Rosado coll’n) ; off Ponta Techobanine (26.68132°S 32.95093°E), - 60–100 m, dredged J. Rosado, xii.2005 (D. Slater coll’n) . SOUTH AFRICA: KwaZulu-Natal: off Kosi River mouth (26.9100°S 32.9433°E), living, - 75 m, sandstone, marine growths, dredged NMDP, RV Meiring Naude, st’n ZA13, 7.vi.1987 (D9009, E1413) ; SE of Kosi estuary mouth (26.9167°S 32.9300°E), - 65 m, sponge, gorgonians, medium sand, dredged NMDP, RV Meiring Naude, st’n ZA12, 7.vi.1987 (D8018) ; off Boteler Point (27.0083°S 32.9117°E), living, - 50 m, coral rubble, lithothamnion, dredged NMDP, RV Meiring Naude, st’n ZB7, 6.vi.1987 (E2943) ; ditto (27.013°S 32.905°E), - 50 m, dead coral rubble, lithothamnion, dredged NMDP, RV Meiring Naude, st’n ZB2, 6.vi.1987 (D9199) ; ditto (27.0117°S 32.9200°E), living, - 70 m, rocks and sand, dredged NMDP, RV Sardinops , st’n ZB19, 6.vi.1990 (S4904, S8715, S8961) ; ditto (27.0133°S 32.9183°E), - 70 m, some coarse sand, some shell rubble, dredged NMDP, RV Meiring Naude, st’n ZB4, 6.vi.1987 (D7415) ; ditto (27.0183°S 32.9200°E), - 78 m, coarse sand, dredged NMDP, RV Meiring Naude, st’n ZB6, 6.vi.1987 (D7475) ; ditto (27.0183°S 32.9183°E), living, - 69–73 m, sponges, rocks and sand, dredged NMDP, RV Sardinops , st’n ZB20, 6.vi.1990 (S5026) ; ditto (27.0400°S 32.9150°E), living, - 75 m, rocks, sand, gorgonians, dredged NMDP, RV Sardinops , st’n ZB22, 6.vi.1990 (S5381) ; ditto (27.0500°S 32.9117°E), - 78 m, marine growths, dredged NMDP, RV Sardinops , st’n ZB23, 6.vi.1990 (S6651) ; off Dog Point (27.1000°S 32.8883°E), living, - 74 m, sandstone rubble and gorgonians, dredged NMDP, RV Sardinops , st’n ZC10, 7.vi.1990 (S6485) ; ditto (27.1083°S 32.8817°E), living, - 70 m, sandstone conglomerate, dredged NMDP, RV Meiring Naude, st’n ZC3, 4.vi.1987 (D6477, E1743) ; ditto (27.1267°S 32.8733°E), living, - 76 m, sandstone rubble and gorgonians, dredged NMDP, RV Sardinops , st’n ZC12, 7.vi.1990 (S8968) ; off Rocktail Bay (27.1850°S 32.8483°E), - 100 m, sand, dredged NMDP, RV Sardinops , st’n ZD4, 7.vi.1990 (S5182) ; ditto (27.1900°S 32.8500°E), - 100 m, sandstone rubble, dredged NMDP, RV Meiring Naude, st’n ZD1, 4.vi.1987 (D7597) ; ditto (27.1900°S 32.8433°E), living, - 75 m, sandstone rubble, dredged NMDP, RV Meiring Naude, st’n ZD2, 4.vi.1987 (D6361, D9154) ; SE of Rocktail Bay (27.1917°S 32.8400°E), living, - 78 m, sandstone rocks, dredged NMDP, RV Sardinops , st’n ZD10, 8.vi.1990 (S4639) ; ditto (27.2017°S 32.8300°E), living, - 60 m, coarse sand, dredged NMDP, RV Sardinops , st’n ZD9, 8.vi.1990 (V894) ; NE of Lala Neck (27.2150°S 32.8283°E), living, - 66–71 m, coarse sand, sandstone rocks, dredged NMDP, RV Sardinops , st’n ZD7, 8.vi.1990 (S6137) ; off Lala Neck (27.2292°S 32.8217°E), living, - 72 m, slightly muddy sand with pennatulids, dredged NMDP, RV Sardinops , st’n ZDD1, 7.vi.1990 (S7335) ; SE of Lala Neck (27.2433°S 32.8133°E), living, - 74 m, sandstone rocks, dredged NMDP, RV Sardinops , st’n ZDD2, 7.vi.1990 (S7232) ; off Hully Point (27.343°S 32.778°E), living, - 60 m, shell rubble, dredged NMDP, RV Meiring Naude, st’n ZF4, 5.vi.1987 (D7332) ; off Sodwana Bay (27.530°S 32.717°E), living, - 70 m, coral rubble, dredged NMDP, RV Sardinops , st’n ZH22, 2.vi.1990 (W7477) ; off Jesser Point (27.5467°S 32.7100°E), living, - 68 m, sponge, coral rubble, dredged NMDP, RV Meiring Naude, st’n ZH3, 3.vi.1987 (D6512) ; ditto (27.5533°S 32.7133°E), living, - 85 m, sponge, coral rubble, dredged NMDP, RV Meiring Naude, st’n ZH4, 3.vi.1987 (D6789) ; off Sodwana Bay (27.5567°S 32.7133°E), - 77 m, dead coral rubble, dredged NMDP, RV Sardinops , st’n ZH19, 2.vi.1990 (S4781) ; ditto (27.5833°S 32.6967°E), - 70 m, medium sand, dredged NMDP, RV Meiring Naude, st’n ZH16, 9.vi.1987 (D8441) ; Leadsman Shoal (27.8000°S 32.6167°E), - 100 m, dredged A.D. Connell, iv.1980 (B4054) ; off Gipsy Hill (27.8117°S 32.6567°E), - 100–125 m, broken shell, dredged NMDP, RV Meiring Naude, st’n ZK9, 11.vi.1988 (E3248) ; SE of Mission Rocks (28.2917°S 32.5433°E), - 50 m, old coral rubble, lithothamnion, dredged NMDP, RV Meiring Naude, st’n ZN1, 10.vi.1988 (E4640).

Distribution and habitat ( Fig. 20 ): Islands of the western Indian Ocean (southern Seychelles group and Mascarenes) and the Mozambique Channel south to north-eastern South Africa (28.3°S, off Mission Rocks); - 35–195 m (living specimens - 50–85 m). In Zululand this species appears to inhabit hard substrata beyond the line of the near-shore reef system, where the sea floor is composed of fragmented sandstone or coral rubble, and is generally rich in marine life. Evidently a mid to outer continental shelf species throughout its range and not part of the shallow-water coral reef biota.

Remarks: This species is very similar to Euchelus ringens Schepman, 1908 from the Sulu Archipelago, Indonesia, and the two may eventually prove to be synonyms. The columella lip of the holotype of E. ringens ( Fig. 68A, B ) is somewhat damaged (perhaps due to occupation by a hermit crab) and looks rather deformed. Compared with south-western Indian Ocean material it differs in being slightly less elevated and in having a narrower umbilicus; there are also minor differences in terms of coloration and aperture characters. In the absence of data on variation in Indonesian material, I have chosen, to err on the side of caution and maintain Ascetostoma providentiae as a distinct species. There can be no doubt, however, that E. ringens is also a species of Ascetostoma .

A. providentiae is easily distinguished from the other southern African chilodontid taxa by its rounded whorl profile, very strong, complex apertural dentition and patent, callus lined umbilicus. ‘ Clanculus ’ crassilabrum Sowerby, 1905 ( Fig. 68C, D ) from Sri Lanka has a similar overall facies, but lacks the unusual umbilical features of Ascetostoma and is probably closer to Herpetopoma .Also similar is Herpetopoma rubrum (A. Adams, 1853) , from Japan to SE Asia, which is likewise often vividly coloured, but in that species the inductural callus does not extend over the umbilical region and the umbilicus remains conventionally patent even at full apertural maturity. The Japanese Euchelus lischkei Pilsbry, 1904 also resembles A. providentiae in size, shape and sculpture, but has a much weaker basal columella tooth and has a simple, patent umbilicus. The Philippine material identified under this name (as Clanculus ) by Kosuge and Chino (1998) is not in fact referable to this species.

The Cretaceous Chilodonta (Agathodonta) africana Rennie, 1930 from the Pondoland coast, Eastern Cape (holotype, SAMC 8630) is superficially similar to A. providentiae , but it has finer granules above the periphery, distinct prosocline pliculae below the suture and a smoother base. It has a well-developed tubercle on the basal lip separated from the columella by a U-shaped notch, but no details of its umbilicus are apparent.

Figures

Fig. 4. Operculum morphology in the Chilodontidae: (A) Littorina littorea (Linnaeus, 1758), Cancale, Brittany,France,max.diameter 10.2mm (NMSA G778);(B) Euchelus asper (Gmelin,1791),Bombay, India,max.diameter 9.0 mm (NMSA J8066);(C) Granata sulcifera, Mtwalume,KZN, max.diameter 3.58 mm (NMSA V3927); (D) Clypeostoma salpinx, off Whale Rock, Eastern Cape, max. diameter 2.59 mm (NMSA C9502); (E) Danilia textilis, max. diameter 2.97 mm (holotype, NMSA E7756/ T2595); (F) Ascetostoma providentiae, off Boteler Point, KZN, max. diameter 2.52mm (NMSA S4904); (G) Herpetopoma (s.s.) instrictum, Low Isles, GreatBarrier Reef, Queensland,max.diameter 3.17 mm (AMS C.304699); (H) H. (s.s.) scabriusculum, Bradleys Head, Sydney Harbour,Australia, max. diameter 1.78 mm (AMS C.30695); (I) H. (s.l.) helix, off Umzinto, KZN, max. diameter 1.01 mm (NMSA D5427); (J) Vaceuchelus cretaceus, SE of Kosi Bay, KZN, max. diameter 2.52 mm (paratype, NMSA S4006/T2638); (K) V. natalensis, off Umzinto, KZN, max. diameter 0.99mm (NMSA D5428); (L) V.semilugubris, Réunion, max. diameter 1.28 mm (M.Jay coll’n MNHN); (M) Perrinia angulifera, off Boteler Point, KZN, max. diameter 4.44 mm (NMSA D9209); (N) P.konos, off Port Grosvenor, Eastern Cape, max. diameter 1.23 mm (NMSA E177); (O) P.stellata, Kosi Bay main coral reef, KZN, max. diameter 1.14 mm (NMSA S1985).

Fig.5. Living animals:(A) Ascetostoma providentiae (Melvill,1909),off Boteler Point, KZN, shell diameter 7.3 mm (NMSA S8961); (B) Perrinia angulifera (A.Adams, 1853), NE of Liefeldt’s Rocks, KZN, shell length 12.8 mm, left cephalic tentacle damaged (NMSA E4344).

Fig.6. External anatomy of Chilodontidae.Schematic illustrations of the external features of the head-foot, viewed from above:(A)Ascetostoma providentiae (Melvill,1909);(B) Clypeostoma salpinx (Barnard, 1964); (C) Danilia textilis sp.n.; (D) Granata sulcifera (Lamarck,1822); (E) Perrinia angulifera (A. Adams, 1853); (F) Vaceuchelus cretaceus sp. n.; (G) V. natalensis (Smith, 1906).

Fig. 18. Ascetostoma providentiae (Melvill, 1909): (A–C) adult specimen cleaned of encrustations, SE of Lala Neck, KZN, length 8.8 mm (NMSA S7232); (D) depressed specimen, off Rocktail Bay, KZN, length 7.2 mm (NMSA D9154); (E) sponge-encrusted specimen, off Rocktail Bay, KZN, length 7.7 mm (NMSA D9154); (F) juvenile specimen, off Dog Point, KZN, diameter 6.25 mm (NMSA S8968); (G, H) paratype of Euchelus providentiae Melvill, 1909, length 6.6 mm, diameter 5.9 mm (NHMUK 1910.3.17.2–3).

Fig.19.Ascetostoma providentiae (Melvill, 1909):(A) oblique view of aperture showing complex dentition and deep umbilical cavity [shell exterior encrusted with sponge], off Lala Neck, KZN, bar = 2.5 mm (NMSA S7335); (B) microsculpture on penultimate whorl, off Boteler Point, KZN, bar = 200 µm (NMSA E2943); (C) protoconch with angular projection on terminal lip, off Dog Point, KZN, bar = 100 µm (NMSA E1743); (D, E) radula, off Lala Neck, KZN, bars = 100 µm and 25 µm respectively (NMSA S7335).

Fig. 20. Distribution of Ascetostoma providentiae. Each triangle represents one or more records.

Fig.68.Ascetostomaand Herpetopoma species examined forcomparison:(A,B) Euchelus ringens Schepman, 1908, holotype, Sulu Archipelago, Indonesia, length 7.8 mm, diameter 7.5 mm [not length 7.5 mm, diameter 8.0 mm as given bySchepman] (ZMAN 3.08.092); (C, D)Clanculus crassilabrum Sowerby, 1905,one of three syntypes,specimen marked with an X, Sri Lanka, length 7.0 mm, diameter 6.4 mm (NHMUK 1905.10.23.41–43); (E, F) Monodonta exasperata A.Adams, 1853, one of four syntypes, Sibonga Is. [Cebu], Philippines, length 6.0 mm, diameter 6.5 mm (NMHUK 196875).