Cremnoconchus agumbensis, 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 : 121-124

CREMNOCONCHUS AGUMBENSIS SP. NOV.

( FIGS 4H , 5M, N, 8, 11M–P, 13C, D, 14A–C, 16E)

Types: Holotype ZSI / WGRS /IR.INV-2313 (Fig. 11M, N); 2 paratypes ZSI / WGRS /IR.INV-2314, 2315 (Fig. 11O, P); Someshwara to Agumbe road, Udupi Dist., Karnataka, India (13.49342°N, 75.07783°E).

Etymology: From the type locality.

Diagnosis: Shell high turbinate, shoulder angled or with rib; pseudumbilicus absent; surface dull, with strong microstriae. Operculum calcified, no internal ridge. Penis large, with distal glandular thickening, stout filament. Western Karnataka State.

Shell ( Figs 4H , 11M–P): Shell H 5.5–10.4 mm. Shape ( Table 1) high turbinate; whorls strongly angled at shoulder (sometimes raised as a rib; Fig. 11N), giving pronounced sutural ramp or channel, but becoming weak at end of last whorl; slight angle at periphery; suture impressed; apex slightly eroded; base slightly swollen. Columella narrow. Pseudumbilicus absent. Surface with single narrow rib at shoulder; dull, with irregular but distinct microstriae, fainter on last whorl and on base ( Fig. 4H ). Protoconch ( Fig. 16E ) 1.5 whorls; diameter 0.68 mm; diameter of first whorl 0.53 mm (n = 1). Colour: dark brown, darker on spire, three more or less distinct broad black-brown bands at shoulder, above periphery and on inner part of base; aperture pale brown, columella and interior bands purple-brown.

Animal: Head, tentacles and sides of foot black, paler at tip of snout. Gills: up to 50 leaflets; unpigmented. Operculum ( Table 1; Fig. 5M, N): opercular ratio 0.439 –0.565; calcified, no internal ridge. Penis (Fig. 14A, B): relatively large; unpigmented; base wrinkled, strap-shaped, with slightly thickened distal glandular region; filament relatively stout, protruding in ethanol-fixed specimens. Pallial oviduct (Fig. 14C): as for genus. One pallial oviduct contained two eggs 0.40 mm diameter (ethanol fixed).

Radula ( Fig. 13C, D ): Relative radula length 1.09– 1.79. Rachidian: length/width 1.19–1.42; 5 cusps (+ 1 outer denticle on either side). Lateral: 6 cusps (sometimes + 1 inner denticle). Inner marginal: 5 cusps (sometimes + 1 inner denticle). Outer marginal: 4 cusps (sometimes + 1 inner denticle). Major cusp of each of 5 central teeth elongate-triangular with rounded and slightly papillose tip; other cusps pointed.

Range ( Fig. 8 ): Western Karnataka State, Agumbe (75 km north-northeast of Mangalore). Records ( Supporting Table S1): Karnataka State: Someshwara to Agumbe road ( ZSI / WGRS /IR.INV-2313, 2314, 2315) .

Habitat and ecology: Damp rock face shaded by evergreen forest. Altitude 379 m.

Remarks: Among the known Cremnoconchus species of Karnataka, C. agumbensis is the only one with turreted whorls produced by a sharp angulation (or rib) at the shoulder, and without a pseudumbilicus ( Table 4). In these characters it resembles the canaliculate form of C. canaliculatus from Maharashtra (Table 3; Fig. 9P, R, U–Z, CC), but that has a more solid shell and the penis bears a drum-shaped gland ( Fig. 10I–N).

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 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.

Figure 16. Radula (A, B) and protoconchs (C–F) of Cremnoconchus species. A, B, C. dwarakii (two views of radula, flat and at 45°), Hulikal Ghat, Udupi Dist., Karnataka (shell H = 6.4 mm). C, C. syhadrensis, Matheran, Raigad Dist., Maharashtra. D, C. canaliculatus, 10 km west of Mahabaleshwar, Raigad Dist., Maharashtra. E, C. agumbensis, Agumbe, Udupi Dist., Karnataka. F, C. dwarakii, Hulikal Ghat, Udupi Dist., Karnataka. Scale bars A, B = 50 Mm; C–F = 0.5 mm. White arrowhead marks junction of protoconch and teleoconch.