Clypeostoma reticulatum, 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 : 401-403

Clypeostoma reticulatum sp. n.

Figs 8 , 9

Etymology: From Latin reticulatus (netted); in reference to the cancellate, net-like sculpture.

Description:

Shell: Large for the genus (length up to 16.7 mm), trochoid-turbiniform, with conical spire and relatively deep, globose last adult whorl (L/D=1.38–1.44, last adult whorl 0.70–0.74 of shell length); teleoconch of up to 6 whorls; first two whorls rounded, whorls 3–4 more or less flat-sided, subsequent whorls convex; apical angle 69–74°; suture of spire whorls level with and mostly covering subperipheral cord of preceding whorl, demarcated by a well-developed channel below peripheral cord; shell periphery rounded. First teleoconch whorl worn in all available specimens, but traces of curved axial pliculae remaining; 3 spiral cords arise during second whorl, with a fourth appearing below adapical suture toward end of whorl; abapical (peripheral) cord strongest; cords crossed by axial pliculae and beaded at intersections; a fifth cord arising below subsutural cord during third whorl (sometimes a sixth during fourth whorl), penultimate whorl thus with 5–6 spiral cords, an additional cord becoming evident level with abapical suture; sculpture remaining similar but strengthening on fourth and subsequent whorls; beads on subsutural cord developing in to angular nodules (25–30 on last adult whorl); intervals between cords slightly wider than cords themselves (that below peripheral cord widest) and crossed by axial pliculae creating quadrate interstices; alignment of pliculae from interval to interval somewhat variable and irregular due to intercalation of additional pliculae, but general pattern of sculpture clearly reticulate, particularly on spire whorls; beads stronger and axially elongated on latter part of last adult whorl; sutural cord of spire whorls may emerge above suture toward end of last adult whorl. Base rounded with 4–6 spiral cords, the last small and partly concealed by reflected lip of aperture; basal cords somewhat more finely beaded than those above periphery. Peristome markedly oblique, more or less in one tangential plane; aperture subcircular to roundly quadrate; columella lip robust, with 2 relatively massive teeth, the upper one slightly more robust, the lower one somewhat narrower and with a small denticle on its lower margin; parietal and umbilical region covered with well-developed, glossy callus which flares outward over base; callus porcelaneous and mostly smooth, but with some beads of unequal size in region adjacent to columella teeth; one particularly strong bead at base of lower columella tooth; edge of callus raised and flaring where it joins flared margin of outer lip. Outer lip lacking an external varix, but somewhat thickened internally and strongly flaring, with 9 labral denticles; denticle nearest base of columella largest and peg-like, separated from basal columella tooth by a U-shaped notch; remaining labral denticles representing the ends of in-running spiral ridges extending deep into aperture, where there may be additional intermediary ridges; similar ridges present inside parietal portion of aperture; denticle at end of uppermost labral spiral ridge comprises a somewhat disjunct swelling, itself with 2 or 3 smaller granules; ridge below this ending in a single large elongate denticle.

Microsculpture: No fresh material available; all traces of intritacalx lost, but some evidence of scratch-like microsculpture present on later whorls.

Protoconch: Missing in all available specimens.

Colour: Shell mostly uniform cream-white to dirty buff, with some pale orange-brown spotting, particularly on subsutural and basal cords.

Dimensions: Holotype, length 16.4 mm, diameter, 11.4 mm; largest specimen, length 16.7 mm.

Operculum, radula and external anatomy: Unknown.

Holotype ( Fig. 9A, B ): MOZAMBIQUE: Mozambique Channel , Almirante Leite Knolls (26.200°S 35.033°E), - 228–230 m, Campagne MAINBAZA, st’n DW3167, dredged RV Vizconde de Eza, 16.iv.2009 ( MNHN 24646 ).

Paratypes: Same data as holotype ( MNHN 24647 , 4 specimens, of which 3 adult, 1 juvenile) .

Distribution and habitat ( Fig. 8 ): Known only from Almirante Leite Knolls, approx. 250 km due east of Maputo, Mozambique, - 228–230 m; rocky substrata with corals, sponges and gorgonians ( Fraussen & Rosado 2011).

Remarks: This species is distinctive amongst south-western Indian Ocean chilodontids on account of its relatively large size, coarse sculpture and well-developed apertural dentition. The most similar species is Clypeostoma elongata ( Vilvens, 2001) from Indonesia and the Philippines, but that species is still larger (adult length over 19 mm), has a more acute apical angle (<60°), a less rounded last adult whorl and only four spiral cords on the spire whorls. In addition, the aperture is transversely elongate and the lower columella tooth is larger than the upper one and bears additional denticles. C. reticulatum shows some variation in the strength of the sculpture (coarseness of reticulation), but this may in part be caused by damage to the outer lip during growth and the subsequent intercalation of additional spiral cords.

That this species has not been found off the Zululand coast of South Africa, a relatively well sampled area not far removed from the type locality, indicates that the isolated Almirante Leite Knolls (a volcanic seamount with numerous craters, rising from -1100 to - 80 m) provide habitats of a different nature to those occurring on the continental shelf and upper slope. The station from which this material was obtained also contained an undescribed species of Bolma ( Alf et al. 2010) and two new buccinid species ( Fraussen & Rosado 2011), and many other new species of benthic invertebrates have been obtained from the locality as a whole (Bouchet pers. comm.), some of which have already been named ( Cabezas et al. 2010; Komai & Chan 2010; Richer de Forges 2010).

Figures

Fig. 8. Distribution of Clypeostoma species in the south-western Indian Ocean. C. meteorae (squares), C. cf. nortoni (circles), C. reticulatum (cross) and C. salpinx (triangles). Each symbol represents one or more records.

Fig. 9. Clypeostoma reticulatum sp. n., Almirante Leite Knolls, Mozambique Channel: (A, B) holotype, length 16. 4 mm (MNHN); (C, D) paratype, length 16. 3 mm (MNHN).