Cremnoconchus globulus, 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 : 121

CREMNOCONCHUS GLOBULUS SP. NOV.

(FIGS 2E, 4F, 5K, L, 8, 11H–L, 12H–L, 13A, B)

Types: Holotype ZSI / WGRS /IR.INV-2310 (Fig. 11I, J); 2 paratypes ZSI / WGRS /IR.INV-2311, 2312 (Fig. 11K); Lesser Kadambi Falls , Chikmagalur Dist., Karnataka, India (13.24384°N, 75.17056°E).

Etymology: Latin globulus , globular, in reference to shell shape.

Diagnosis: Shell globular, without ribs; pseudumbilicus moderate, sometimes perforated; surface with satin sheen, no microstriae. Operculum weakly calcified, no internal ridge. Penis with lateral glandular flange, slender filament. Western Karnataka State.

Shell ( Figs 4F , 11H–L): Shell H 6.0– 8.8 mm. Shape ( Table 1) globular; whorls rounded, without angulation; suture impressed; apex eroded; base slightly swollen. Columella moderately narrow, wider at base. Pseudumbilicus moderate (to 0.8 mm), sometimes perforated, outlined by angled margin, sometimes forming a slight rounded rib. Surface almost always without ribs above periphery; rarely a slight thickening or indistinct rib near suture. Surface with satin sheen; spiral striae almost or entirely absent ( Fig. 4F ). Diameter of first whorl 0.50–0.66 mm (N = 3). Colour: dark brown or olive-brown, sometimes darker on spire and in band at suture; columella and umbilicus purple-brown; aperture pale brown to whitish, with sutural band showing through.

Animal: Head, tentacles, and sides of foot pale grey to black, tentacles darker, paler at tip of snout. Gills: up to 40 leaflets; black. Operculum ( Table 1; Fig. 5K, L): opercular ratio 0.364 –0.421; weakly calcified, dark red-brown, no internal ridge. Penis ( Fig. 12H–L ): unpigmented or slightly pigmented; base wrinkled, with long thickened flange running across left side towards eye, glandular knob on right side, and slight glandular swelling distally (sometimes opaque); invagination about half length of base in ethanol-fixed specimens; filament slender, rarely protruding in ethanol-fixed specimens. Pallial oviduct: as for genus.

Radula ( Fig. 13A, B ): Relative radula length 2.66– 3.43. Rachidian: length/width 1.10–1.22; 5 cusps (+ 1 outer denticle on either side). Lateral: 5 cusps (+ 1 inner denticle). Inner marginal: 5 cusps. Outer marginal: 4–5 cusps. Major cusp of each of 5 central teeth triangular leaf-shaped with pointed to slightly rounded tip; other cusps pointed.

Range ( Fig. 8 ): Western Karnataka State, Kudremukh (55 km north-east of Mangalore). Records (see Supporting Table S1): Karnataka State: Lesser Kadambi Falls (ZSI/WGRS/IR.INV-2310, 2311, 2312); Greater Kadambi Falls (ZSI/WGRS/IR.INV-2308, 2309).

Habitat and ecology: Common in film of water flowing over rock face beside waterfall (Fig. 2E); on stones in shallow streams (to 30 cm deep) with fast-flowing water; in partial shade of riparian vegetation in wet evergreen forest. Altitude 941 and 967 m.

Remarks: Four Cremnoconchus species have similar umbilicate, globular to turbinate, smooth shells ( Table 4). Cremnoconchus globulus is distinguished by its lack of a basal rib (present in C. cingulatus ), moderate pseudumbilicus and weakly calcified operculum (well calcified in C. castanea ). Distinction from C. hanumani , with which it occurs in the same microhabitat, is discussed in the Remarks on that species. The penes of all four are diagnostic ( Figs 12 , 14, 15).

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 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 12. Anatomy of Cremnoconchus hanumani (A–G) and C. globulus (H–L), all to same magnification. A–L, penes (all fixed in ethanol); F, G are intact and sectioned views of same penis. A–C, Hanuman Gundi Falls, Chikmagalur Dist., Karnataka (ZSI/WGRS; shell H: A = 4.9 mm; B = 3.5 mm; C = 3.3 mm). D–G, Greater Kadambi Falls, Chikmagalur Dist., Karnataka (ZSI/WGRS; shell H: D = 3.9 mm; E = 4.0 mm; F, G = 5.0 mm). H–K, Lesser Kadambi Falls, Chikmagalur Dist., Karnataka (ZSI/WGRS; shell H: H = 7.0 mm; I = 6.0 mm; J = 7.0 mm; K = 6.3 mm). L, Greater Kadambi Falls, Chikmagalur Dist., Karnataka (ZSI/WGRS; shell H = 7.9 mm). Shading conventions as in Figure 6.

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.