Vaceuchelus cretaceus, 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 : 447-452

Vaceuchelus cretaceus sp. n.

Figs 4J , 6F , 39–41

Euchelus scrobiculatus [non Souverbie, 1866]: Jay 2009.

Etymology: From Greek creta (white earth or chalk); in reference to the superficial chalk-like intritacalx deposit on the shell.

Description:

Shell: Small, but relatively large for genus; elevated-turbiniform (L/D=1.0–1.25); teleoconch of 4.5–5.0 whorls; sculpture initially strongly cancellate, becoming foveolate with growth; spire truncate and protoconch sunken; first teleoconch whorl initially sculptured only by rib-like axial pliculae, 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 and pliculae thickening considerably during third whorl and becoming less well defined; intermediary cords absent, with the exception of a fourth cord which usually develops on shoulder during third teleoconch whorl; intervals between cords wider than cords themselves; cords and pliculae interact to produce low conical granules where they cross; last adult whorl with 15–20 pliculae, those behind outer lip usually poorly defined or obsolete; pliculae narrower than cords on early whorls, more or less equal to them on last adult whorl; interstices distinctly quadrate apically, but becoming more rounded and pit-like (foveolate) on last adult whorl; strong growth flaws frequently present on last adult whorl. Base with 3 spiral cords, one level with suture, one marking edge of umbilicus and another between these; interval between outer and middle cords usually broader and with only weakly developed pits, that between middle and inner cords narrower and more strongly pitted; an additional cord is evident within umbilicus of young juveniles, but this becomes obscured with growth; umbilicus usually narrowly patent even in adults, occasionally closed; relatively wider in juveniles. Peristome oblique; aperture subcircular; columella concave with a broad rounded swelling at its base; swelling non-nacreous and rather variable in size; interior of aperture nacreous when fresh, lacking ridges or denticles inside outer lip.

Microsculpture ( Fig. 40B, C ): Rather poorly defined and mostly covered by intritacalx deposit in fresh specimens; surface of apical whorls appearing etched, but with some traces of vermiform spiral threads; later whorls with close-set, shallow, prosocline, scratch-like marks.

Protoconch ( Fig. 40C ):White; diameter ca 200 µm; sunken; apex very slightly pinched in; terminal lip with a well-developed trigonal projection; superficial sculpture well developed, arranged in irregular axial lines, spiral element scarcely evident.

Colour: Fresh specimens milky-white with a relatively thick, chalky, white to pale buff or ashy-grey intritacalx deposit; deposit usually somewhat eroded.

Dimensions: Holotype, length 7.6 mm, diameter 6.6 mm; largest specimen (NMSA S4006), length 8.65, diameter 6.9 mm.

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

Radula ( Fig. 40 D, E ): Formula ∞+3+1+3+∞; ca 45 transverse rows of teeth; transition from lateral to marginal series not well delineated. Rachidian with well-developed hood and narrowly trigonal cusp; cusp with small medial indentation near its base; cutting edge with a dominant, lanceolate central denticle, with 2 or 3 smaller denticles on each side. Only 3 lateral teeth evident, the fourth tooth is longer and lacks the robust, alate shaft of the laterals, and I consider it to be a marginal; lateral tooth cusps decreasing slightly in size from first to third, with a large, spathulate central element and smaller lateral denticles on both margins, those on the outer edge coarser. Marginals generally long and very slender, tending to collapse when air dried; inner ones somewhat shorter with a rather weakly and irregularly dentate, recurved cusp, and lacking well-developed pectinate denticles on its outer margin.

External anatomy ( Fig. 6F ): Head-foot largely white, cephalic and most epipodial tentacles blackish; some additional dark pigmentation on snout and lips, and on free margin of cephalic lappets (colour lost in alcohol). Cephalic lappets relatively broad, but not meeting in mid-line, free margin with fine projections; snout with well-developed lateral flanges; right post-ocular peduncle present; right subocular tentacle not evident; free margin of left neck lobe more extensively tentaculate than that of right one; approx. 10 epipodial tentacles of varying size on each side; an indistinct epipodial sense organ seemingly present at base of most epipodial tentacles. (Only one preserved specimen available; paratype, NMSA S4006/T2638.)

Holotype ( Fig. 39A–C ): SOUTH AFRICA: KwaZulu-Natal: off Boteler Point (27.00°S 32.92°E), - 70 m, coral rubble, dredged NMDP, RV Meiring Naude, st’n ZB5, 6.vi.1987 ( NMSA E1761 /T2600).

Paratypes: RÉUNION:off St-Paul Bay, Marion-Dufresne 32, st’n DC85 (21°00'S 55°15'E), living, - 58–70m, dredged, 1982 ( MNHN 24655 , 54 specimens) ; Cap la Houssaye , hand-dredged sand, J. Drivas ( NMSA K2756 /T2603) . SOUTH AFRICA: KwaZulu-Natal: SE of Kosi Bay (26.9000°S 32.9250°E), living, - 50 m, coral slabs, dredged NMDP, RV Sardinops , st’n ZA37, 3.vi.1990 ( NMSA S4006 /T2638, 1 specimen) ; SE of Kosi River Mouth (26.9167°S 32.9300°E), - 65 m, sponge, gorgonians, medium sand, dredged NMDP, RV Meiring Naude, st’n ZA12, 7.vi.1987 ( NMSA D8017 /T2602, 1 specimen) ; same data as holotype ( NMSA V2961 /T2639, 3 specimens; NHMUK 20110384 , 1 specimen) ; off Boteler Point (27.0600°S 32.9083°E), - 70 m, sand, some stones, dredged NMDP, RV Sardinops , st’n ZB24, 6.vi.1990 ( NMSA S4157 /T2601, 1 specimen) ; off Boteler Point (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 ( NMSA D7420 /T2636, 1 specimen) ; NE of Dog Point (27.0800°S 32.89167°E), - 65 m, sand, lithothamnion pebbles, dredged NMDP, RV Sardinops , st’n ZC9, 7.vi.1990 ( NMSA S7593 /T2637, 4 specimens) ; off Rocktail Bay (27.1850°S 32.8483°E), - 100 m, sand, dredged NMDP, RV Sardinops , st’n ZD4, 7.vi.1990 ( NMSA S5138 /T2602, 3 specimens) ; off Rocktail Bay (27.1900°S 32.8500°E), - 100 m, sandstone rubble, dredged NMDP, RV Meiring Naude, st’n ZD1, 4.vi.1987 ( NMSA D7598 /T2604, 1 specimen) ; Sodwana Bay (27.5330°S 32.6830°E), - 100 m, dredged CSIR Water Research ( NMSA S9831 /T2607, 1 specimen) ; 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 ( NMSA E4641 /T2605, 1 specimen; E7491/T2608, 3 specimens) .

Additional material examined (all NMSA unless indicated otherwise): RÉUNION: off south-east coast of island, Marion-Dufresne 32, st’n DC1 (21°13'S 55°49'E), - 150–160 m, dredged, 1982 ( MNHN); Réunion, not further localised (M. Jay coll’n, MNHN). MOZAMBIQUE: off Lacerda Lighthouse (25.56167°S 32.84472°E), - 52–55 m, dredged, vi.2010, (J. Rosado coll’n) ; off Inhaca Is. (26.020°S 33.066°E), - 125 m, dredged J. Rosado, ii.2006 (D. Slater coll’n) ; off Ponta Techobanine (26.68132°S 32.95093°E), - 60–135m, dredged J. Rosado, xii.2005 and i.2010 (D. Slater coll’n) . SOUTH AFRICA: KwaZulu-Natal: off Kosi Bay (26.8916°S 32.9266°E), - 51 m, sand, stones large algae, dredged NMDP, RV Sardinops , st’n ZA48, 4.vi.1990 (S4061) ; off Boteler Point (27.0067°S 32.9083°E), - 51 m, sand, some lithothamnion pebbles, dredged NMDP, RV Sardinops , st’n ZB9, 5.vi.1990 (S9668) ; ditto (27.0083°S 32.9117°E), - 50 m, dead coral rubble and lithothamnion, dredged NMDP, RV Meiring Naude, st’n ZB7, 6.vi.1987 (E5263) ; ditto (27.0117°S 32.9200°E), - 70 m, rocks, sand, dredged NMDP, RV Sardinops , st’n ZB19, 6.vi.1990 (S8701) ; ditto (27.0200°S 32.9183°E), - 76 m, lithothamnion pebbles, sand, dredged NMDP, RV Sardinops , st’n ZB15, 5.vi.1990 (S7550) ; NE of Dog Point (27.0800°S 32.8867°E), - 56–57 m, sand, lithothamnion pebbles, dredged NMDP, RV Sardinops , st’n ZC8, 6.vi.1990 (S5052) ; SE of Rocktail Bay (27.2017°S 32.8300°E), - 60 m, coarse sand, dredged NMDP, RV Sardinops , st’n ZD9, 8.vi.1990 (V875) ; off Sodwana Bay (27.5300°S 32.7133°E), - 70 m, dead coral rubble, dredged NMDP, RV Sardinops , st’n ZH18, 2.vi.1990 (S4564) ; ditto (27.4781°S 32.7232°E), - 46 m, sediment at base of drop-off in canyon, dredged UND, Marine Geoscience Unit, 7 xi.1992 (V2609); NE of Liefeldt’s Rocks (27.7200°S 32.6617°E), - 50 m, lithothamnion, stones, some coarse sand, dredged NMDP, RV Meiring Naude, st’n ZJ1, 8.vi.1988 (E4343) ; Leadsman Shoal (27.8000°S 32.6160°E), - 100 m, dredged A.D. Connell, iv.1980 (B4066) ; off Leven Point (27.9167°S: 32.6467°E), - 250 m, coarse sand, dredged NMDP, RV Meiring Naude, st’n ZL5D, 9.vi.1988 (S9427).

Distribution and habitat ( Fig. 41 ): South-western Indian Ocean, known only from Réunion, southern Mozambique and northern Zululand (south to Mission Rocks); shallow subtidal to - 250 m, but mostly shallower than - 160 m (living specimens - 50–70 m); dead shells not uncommon amongst lithothamnion encrusted pebbles and coral rubble in - 50–70 m, beyond the near-shore reef system in northern Zululand.

Remarks: There is no similar species yet reported from the south-western Indian Ocean. V. gemmula , V. jayorum and V. natalensis are much smaller and thinner shelled, lack a basal columella swelling and retain sharply defined spirals and axials throughout. Although they may resemble juvenile V. cretaceus , they have a narrower umbilicus, more evenly spaced cords on the base and a less strongly truncated apex. Furthermore, in these small species the spiral cords are stronger in relation to the axial pliculae and more elevated than they are in V. cretaceus . V. semilugubris is also smaller than V. cretaceus , has denticles inside the outer lip when fully mature and is typically patterned with bold black markings.

This species differs from V. angulatus (Pease, 1868) (type species of Vaceuchelus ) and similar species from the south-western Pacific, such as V. foveolatus (A. Adams, 1853) and V. scrobiculatus (Souverbie in Souverbie & Montrouzier, 1866), in being larger and in lacking denticles or ridges inside the outer lip (cf. figures provided by Herbert 1996). More similar to V. cretaceus are V. cavernosus (Sowerby, 1905) from Sri Lanka ( Fig. 70A, B ) and V. clathratus (A. Adams, 1853) from the Philippines ( Fig. 70C, D ), both of which are of similar size and also lack sculpture inside the outer lip. Nonetheless, they retain a well defined, relatively fine, cancellate sculpture on the last adult whorl and have four and five spiral cords respectively on the base (including that level with suture) as opposed to three in V. cretaceus . Neither possesses the basal columella swelling of V. cretaceus . The most similar species is the recently described Vaceuchelus pagoboorum Poppe, Tagaro & Dekker, 2006 from the Philippines. This is clearly closely related to V. cretaceus and likewise possesses a broad swelling at the base of the columella, but differs in having an additional low rounded tubercle inside the outer lip near its junction with the parietal portion of the aperture, has more evenly spaced basal cords (four in juveniles compared with three in V. cretaceus , but the inner one becomes obsolete in adults), retains distinct pits in the interval between the out- er and middle basal cords, and frequently has brownish markings on the spiral cords. With no material from intermediate localities, it is difficult to assess the significance of these differences, but they seem to constitute characters by which the populations can be distinguished and I thus describe the south-western Indian Ocean material as a new species.

I refer this species to Vaceuchelus with some hesitation. The overall facies of its shell also shows some resemblance to that of Trochus clathratus Aradas, 1847 , type species of Putzeysia Sulliotti, 1889 . In that genus, however, the apex is not flattened, and the protoconch is globose and less strongly sculptured ( Engl & Rolán 2009). The protoconch of V. cretaceus is closer to that of V. natalensis and V. gemmula , but differs in having a distinct projection on the terminal lip. Furthermore, whereas the radula of V. natalensis appears to be simply a reduced version of the Herpetopoma radula, that of V. cretaceus differs in having a narrower, acutely trigonal rachidian cusp and inner marginals that lack a strongly pectinate outer margin. With no comparable information available concerning the type species of Vaceuchelus , these differences are difficult to evaluate, but they suggest a degree of intrageneric variability within Vaceuchelus that merits further study.

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.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. 39. Vaceuchelus cretaceus sp. n.: (A–C) holotype (NMSA E1761/T2600), length 7.6 mm; (D) livecollected specimen with nacreous interior (a severe growth flaw at the beginning of the last whorl has resulted in closure of the umbilicus), SE of Kosi Bay, KZN, length 8.3 mm, paratype (NMSA S4006/T2638).

Fig.40. Vaceuchelus cretaceus sp.n.: (A) SEM of paratype, NE of Dog Point, KZN, length 6.6 mm (NMSA S7593/T2637);(B) adult microsculpture, SE of Mission Rocks,KZN,bar = 250µm (paratype,NMSA E7491/T2608); (C) protoconch, off Rocktail Bay, KZN, bar = 250 µm (paratype, NMSA S5138/ T2602); (D, E) radula, SE of Kosi Bay, KZN (paratype, NMSA S4006/T2638):(D) central field and most of the marginals, bar = 50 µm; (E) rachidian and lateral teeth, bar = 25 µm.

Fig. 41. Distribution of Vaceuchelus cretaceus. Each triangle 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.