Darwininitium shiwalikianum Budha & Mordan, 2012

Budha, Prem B., Mordan, Peter B., Naggs, Fred & Backeljau, Thierry, 2012, Darwininitium - a new fully pseudosigmurethrous orthurethran genus from Nepal (Gastropoda, Pulmonata, Cerastidae), ZooKeys 175, pp. 19-26 : 20-21

Darwininitium shiwalikianum Budha & Mordan, 2012 sp. n.

Material.

Holotype CDZTU0114: Kasara near Tamor Lake, Chitwan National Park, Central Nepal, ca 210 m. 27°61'10"N, 85°20'05"E, sal ( Shorea robusta ) forest, leg P.B. Budha 5 May 2008. Paratype from the type locality, CDZTU0114a/1 shell. Other paratypes CDZTU0115/2: Taubas along the road side of Tribhuvan Highway, Bhainse, left bank of Rapti river, Makwanpur [=district], Central Nepal, ca 520 m. 27°30'13"N, 85°02'59"E, 2 live. Mixed riverine forest, leg P.B. Budha 7 May 2008.

Diagnosis.

Cerastidae with a fully pseudosigmurethrous pallial system including fully enclosed renal and rectal branches of ureter; penial appendix lacking, which is present in all known cerastid genera. Shell carinated, white flecks on a dark-brown background.

Description:

Shell (Figure 2a, 2b): Dextral, globosely turbinate, weakly carinated, rimately perforate, whorls 5, apex blunt, suture shallow, chestnut with wide and irregular shaped radial white patches both in upper- and under- surface, first two whorls smooth but under magnification (60 ×) shallow dotted wrinkles visible, later whorls with weak radial striae, aperture ovate, peristome thin and reflected slightly descended toward the aperture, columellar margin reflected covering nearly half the umbilicus.

Shell dimensions

(mm). Holotype: 13.6 × 15.2 × 12.6, aperture 7.9 × 8.0, whorls 5, paratype from the type locality 14.1 × 13.8 × 12.5, whorls 5, aperture 7.8 × 7.9, paratypes from Taubas 11.7 × 12.5 × 10.6, aperture 6.9 × 7.5, whorls 4.5, 12.3 × 15.7 × 12.9, aperture 8.1 × 10.5, wh. 4.5.

Etymology.

The genus is named as a tribute to the Darwin Initiative for having supported land snail projects and in particular for supporting the senior authors’ participation in the project Developing land snail expertise in South and Southeast Asia from 2006-2011. The species name derives from the Lesser Himalaya Shiwalik range, from where it was reported.

Animal

(Figures 3a, 3b). The anterior of the uniformly pale cream body can extend significantly more than 2 × of the shell length.

Pallial cavity

(Figure 4a). Kidney of the typical orthurethran type, running approximately four-fifths the length of the pulmonary cavity; a thin-walled, completely closed tube runs from the renal pore along the full length of the inner margin of the kidney, folding at the top to run a short distance towards the rectum, and then down along the inner margin of the rectum, again as a fully closed tube, almost as far as the anus and close to the pneumostome, where it opens with a slight flare. Pallial venation is prominent and a mantle gland is lacking.

Reproductive system

(Figures 4b, 4c). The female system has a well-developed gametolytic sac with a long peduncle with an expanded basal portion, and darkly pigmented spongy tissue in the atrium and at the base of the free-oviduct. The penis lacks an appendix, but has a prominent epiphallar caecum. The penial retractor inserts well below and opposite the point of insertion of the vas deferens. Internally the penis is separable into two regions, the lower having numerous longitudinal pilasters with a knobbly appearance. Above there is a slight constriction of the lumen by an undulating ring pilaster with a smooth, forked pilaster above, running downwards from the level of the opening of the vas deferens. The epiphallus has a thick pad of transverse, weakly ridged tissue running down its length more-or-less opposite the pore of the vas deferens, as well as a smooth longitudinal fold which runs down from within the caecum as far as the top of the vas deferens opening. There is no obvious penial sheath. The hermaphrodite duct lacks the clump of diverticulae characteristic of the Enidae sensu stricto.

Distribution.

The genus Darwininitium was collected in the Dun valley of the Lesser Himalaya in the Rapti river basin from an elevation of ca 210 m in Chitwan National Park and extending northward to Taubas, Bhainse Makwanpur, Central Nepal at an elevation of ca 520 m above sea level. The area has a humid, sub-tropical climate and comprises sandstones, siltstones and mudstones. The forest is dominated by tropical sal ( Shorea robusta ) mixed with Terminalia sp. in the national park, and mixed riverine forest with major tree species of Acacia catechu , Dalbergia sissoo , Bombax ceiba along the river belt at Bhainse (Figure 5).