Cremnoconchus castanea, Reid & Aravind & Madhyastha, 2013

Reid, David G., Aravind, Neelavara Ananthram & Madhyastha, Neelavara Ananthram, 2013, A unique radiation of marine littorinid snails in the freshwater streams of the Western Ghats of India: the genus Cremnoconchus W. T. Blanford, 1869 (Gastropoda: Littorinidae), Zoological Journal of the Linnean Society 167 (1), pp. 93-135 : 126-128

CREMNOCONCHUS CASTANEA SP. NOV.

( FIGS 4M , 5Q, R, 11V–AA, 13G, H, 15A–D)

Types: Holotype ZSI / WGRS /IR.INV-2321 (Fig. 11W, X); 1 paratype ZSI / WGRS /IR.INV-2320 (Fig. 11 V); Belkal Thirtha Falls , near Kollur, Udupi Dist., Karnataka, India (13.842°N 74.897°E).

Etymology: Latin castanea , a chestnut, in reference to shell colour, used as a noun in apposition.

Diagnosis: Shell turbinate; ribs absent; pseudumbilicus wide, perforated; surface with indistinct or strong microstriae. Operculum calcified, with internal ridge. Penis large, with distal glandular pad, slender filament. Western Karnataka State.

Shell ( Figs 4M ; 11V–AA): Shell H 4.7–9.4 mm. Shape turbinate; whorls slightly angled at shoulder and periphery; ribs absent; suture impressed; apex eroded; base slightly swollen. Columella narrow. Pseudumbilicus broad, 0.5–1.0 mm, with sharply angled margin, perforated. Surface dull or with satin sheen; indistinct or strong, coarse microstriae cover surface ( Fig. 4M ). Diameter of first whorl 0.32– 0.53 mm (N = 2). Colour: orange-brown to chestnut brown, darker on spire and with indistinct darker band at suture; aperture pale brown, columella pinkish-brown to white.

Animal: Head, tentacles, sides of foot, and body pale grey to black. Gills: unpigmented. Operculum ( Table 1; Fig. 5Q–R): opercular ratio 0.341 –0.450; well calcified, flat, with internal ridge. Penis (Fig. 15A–D): relatively large, unpigmented; base wrinkled, elongate, solid, with large triangular glandular pad on reverse side; invagination about half length of base in ethanol-fixed specimens; filament slender, protruding in ethanolfixed specimens. Pallial oviduct: as for genus.

Radula ( Fig. 13G, H ): Relative radula length 2.37– 2.59. Rachidian: length/width 1.08–1.26 (–1.64); 5 cusps (+ 1 outer denticle on either side). Lateral: 5 cusps (+ 1 inner denticle). Inner marginal: 5 cusps (+ 1 inner denticle). Outer marginal: 4–5 cusps. Major cusp of each of 5 central teeth leaf-shaped with pointed or slightly papillose tip; other cusps pointed.

Range ( Fig. 8 ): Western Karnataka State, near Kollur (110 km north of Mangalore). Records (Supporting Table S1): Karnataka State: Belkal Thirtha Falls (ZSI/WGRS/IR.INV-2320, 2321); Arasinagundi Falls (BMNH 20120032).

Habitat and ecology: Spray zone of strong waterfalls. Large groups found aestivating in crevices during summer at Arasinagundi Falls. Altitude 373– 384 m.

Remarks: Four species ( C. castanea , C. cingulatus , C. globulus , C. hanumani ) from Karnataka show similarities in their turbinate to globular shells

› Figure 15. Anatomy of Cremnoconchus castanea (A–D) and C. dwarakii (E–J), all to same magnification. A–D, E–I, penes (A, live, relaxed; B, C, live, contracted; D–I, fixed in ethanol); B, C, are abaxial and adaxial views of same penis; G, H, are abaxial and sectioned views of same penis. J, pallial oviduct. A–C, Arasinagundi Falls, Udupi Dist., Karnataka (BMNH 20120034; shell H: A = 7.6 mm; B, C = 4.7 mm). D, Belkal Thirtha Falls, Udupi Dist., Karnataka (ZSI/WGRS; shell H = 7.0 mm). E–J, Hulikal Ghat, Udupi Dist., Karnataka (ZSI/WGRS; shell H: E = 6.4 mm; F = 6.2 mm; G, H = 6.1 mm; I = 6.9 mm; J = 6.9 mm). Shading conventions as in Figure 6 .

without ribs on their upper surface. Details of the relative size of the pseudumbilicus and degree of calcification of the operculum can aid discrimination, but penial shape is most useful ( Table 4). Of these four, only C. castanea is known to develop strong, coarse microstriae, but these can sometimes be indistinct. The combination of large umbilicus and strong microstriae is similar to some examples of C. canaliculatus from Maharashtra (Fig. 9AA–EE), but that species has a basal drum-shaped gland on the penis ( Fig. 10I–N).

An additional unlocalized sample (ZSI/WGRS/ IR.INV-2322) could belong to this species. The shells (Fig. 11Z, AA) differ in that the pseudumbilicus, while perforated, is narrower than in the shells described above (0.3–0.5 mm in shells with H = 4.3–5.6 mm; Fig. 11V–Y) and has a rounded (not sharp) edge. Shell and operculum are otherwise similar. Only a single penis was seen and this was similar to those described.

Figures

Figure 4. Microsculpture of Cremnoconchus species (viewed by SEM). A, C. dwarakii, Hulikal Ghat, Udupi Dist., Karnataka. B, C. syhadrensis, Matheran, Raigad Dist., Maharashtra. C, C. syhadrensis, Khandala, Pune Dist., Maharashtra. D, C. conicus, 44 km west of Bhor, Pune Dist., Maharashtra. E, C. conicus, 6 km west of Mahabaleshwar, Satara Dist., Maharashtra. F, C. globulus, Lesser Kadambi Falls, Chikmagalur Dist., Karnataka. G, C. cingulatus, Hulikal Ghat, Udupi Dist., Karnataka. H, C. agumbensis, Agumbe, Udupi Dist., Karnataka. I, C. canaliculatus, 10 km west of Mahabaleshwar, Raigad Dist., Maharashtra. J, C. canaliculatus, Dongarwadi, Tamhini, Pune Dist., Maharashtra. K, C. canaliculatus, 5 km south of Mahabaleshwar, Satara Dist., Maharashtra. L, C. castanea, Belkal Thirtha Falls, Udupi Dist., Karnataka. M, C. castanea, Arasinagundi Falls, Udupi Dist., Karnataka. N, C. hanumani, Greater Kadambi Falls, Chikmagalur Dist., Karnataka. O, C. hanumani, Hanuman Gundi Falls, Chikmagalur Dist., Karnataka.

Figure 6. Anatomy of Cremnoconchus syhadrensis. A, B, D–G, penes (A, E–F, fixed in ethanol; B, D, live). E–G are three views of single penis, external (E), with base sectioned (F), and with coiled penial vas deferens displaced to the right to show retractor muscle and with filament sectioned to show continuation of vas deferens to its tip (G). C, pallial oviduct and egg removed from straight section. A, Matheran, Raigad Dist., Maharashtra (BMNH 20120035; shell H = 7.4 mm). B, C, E–G, Matheran, Raigad Dist., Maharashtra (ZSI/WGRS; shell H: B = 7.2 mm; C = 7.2 mm; D = 5.8 mm; E–G = 7.5 mm). D, Khandala, Pune Dist., Maharashtra (ZSI/WGRS). Abbreviations and shading conventions: b, copulatory bursa (dashed outline, visible by transparency); c, cavity surrounding penial vas deferens and retractor muscle (black); d, distal to this point the penial vas deferens is tightly bound to the sheath of the retractor muscle; e.g. egg groove visible by transparency (thick line); f, penial filament; g, opaque glandular region of penial base (medium stipple); gc, firm gelatinous coating of mature egg; i, invagination of penial base (shaded); o, position of terminal opening of pallial oviduct into mantle cavity; oag, opaque part of albumen gland (dense stipple); ov, ovum; pvd, penial vas deferens; rm, retractor muscle of penial filament; ss, straight section of pallial oviduct; tag, translucent region of albumen gland (sparse stipple).

Figure 8. Distribution of Cremnoconchus species (solid circles). Two or more species names (e.g. syhadrensis + canaliculatus) indicate sympatric occurrence. See Supporting Table S1 for locality details. The shaded area is the Western Ghats region as defined by Irfan-Ullah & Davande (2008). Cities indicated by asterisks.

Figure 13. Radulae of Cremnoconchus species (two views of each radula, flat and at 45°). A, B, C. globulus, Lesser Kadambi Falls, Chikmagalur Dist., Karnataka (ZSI/WGRS; shell H = 7.4 mm). C, D, C. agumbensis, Agumbe, Udupi Dist., Karnataka (ZSI/WGRS; shell H = 9.5 mm). E, F, C. cingulatus, Hulikal Ghat, Udupi Dist., Karnataka (ZSI/WGRS; shell H = 5.7 mm). G, H, C. castanea, Arasinagundi Falls, Udupi Dist., Karnataka (ZSI/WGRS; shell H = 8.5 mm). Scale bars = 50 Mm.