Rishetia tribhuvana Budha

Budha, Prem B., Naggs, Fred & Backeljau, Thierry, 2017, Conchological differentiation and genital anatomy of Nepalese Glessulinae (Gastropoda, Stylommatophora, Subulinidae), with descriptions of six new species, ZooKeys 675, pp. 129-156 : 139-140

Rishetia tribhuvana Budha sp. n. Figs 2K, 12

Material examined.

Holotype: CDZMTU074P/1 specimen, Tribhuvan University garden, Kirtipur, Kathmandu, Nepal, 1320 m, 27.680203N, 85.289154E, 15.VIII.2006, leg. P.B. Budha. Paratypes: CDZMTU074/15 shells and CDZMTU075P/5 specimens (3 dissected) from the type locality, 22.III.2011, leg. P.B. Budha. Paratypes: CDZMTU076/6 shells, Champadevi Forest, Kirtipur, Kathmandu, Nepal, 1680 m, 27.653060N, 85.244785E, 23.VIII.2006, leg. P.B. Budha. Paratypes: CDZMTU077/4 shells, Nagarjun Forest, 1582 m and 1680 m, 27.742616N, 85.293248E, 07.I.2009, 16.I.2009, leg. S. Khanal and S. Khatiwara.

Distribution.

Hill forests of Kathmandu valley, Nepal.

Etymology.

The name refers to the type locality, Tribhuvan University garden

Shell.

Measurements (n = 12): SH 7.5-11.0 mm, SW 2.7-3.0 mm, HA 2.5-3.0 mm, WA 1.4-2.0 mm, Wh 8.5-9.5; holotype: SH 10.1 mm, SW 3.0 mm, HA 2.5 mm, WA 2.0 mm, Wh 9; approx. 3.3 × higher than wide, slender, thin, dull brown. Surface striated with radial fine ribs, much denser on the 3rd and 4th whorls; ribs widely separated on the penultimate and body whorls. The first whorl blunt and smooth. Spire rounded; suture deep. Aperture ovate elliptical; approx. 2 × higher than wide, peristome thin; columellar margin calloused whitish, obliquely truncate at the base.

Genitalia

(n = 4) (Fig. 12). Vas deferens long. Flagellum slightly shorter than the epiphallic caecum. The length of the flagellum nearly two-thirds of that of the epiphallus. The basal part of the penis narrower than the proximal part. The vagina nearly as long as the penis. The penial retractor muscle far apart from the flagellum. The gametolytic sac is rounded and distinct from the gametolytic duct. The hermaphrodite duct is connected at the base of the albumen gland.

Remarks.

R. tribhuvana sp. n. is the smallest Rishetia species in Nepal. Conchologically, it is “intermediate” between R. hastula (Benson, 1860) and R. roberti Godwin-Austen, 1920. R. tribhuvana sp. n. differs from both these species by its weaker radial sculpture compared to R. hastula and its narrower body whorl compared to R. roberti . Moreover, the illustrations of Godwin-Austen (1920, pl. CLXIII, fig. 10) suggest that R. roberti has a rounded first whorl, whereas it is nearly flat in R. tribhuvana sp. n. The flagellum and epiphallic caecum are well-developed and nearly equal in size in R. tribhuvana sp. n., whereas in R. hastula the flagellum is very small and the epiphallic caecum is only a minute-knob. R. tribhuvana sp. n. and R. hastula are known from geographically different locations. The former is a hill species reported above 1300 m, while the latter is known only from the plain below 300 m elevation. R. roberti is also a hill species from Richila peak, Sikkim. The presence of R. tribhuvana sp. n. in the garden of Tribhuvan University is due to a historical connection between this garden and the Champadevi hill Forest, about 4 km south 300-400 m higher from the university premises. This connection has been lost because of human settlement.