Conchological and molecular analysis of the "non-scaly" Bornean Georissa with descriptions of three new species (Gastropoda, Neritimorpha, Hydrocenidae).

Menno Schilthuizen,Mohd Zacaery Khalik,Kasper P. Hendriks,Jaap J. Vermeulen

doi:10.3897/zookeys.840.33326

Abstract

The Bornean representatives of the genus Georissa (Hydrocenidae) have small, dextral, conical, calcareous shells consisting of ca. three teleoconch whorls. Our recent study on the Georissa of Malaysian Borneo has revealed high intra- and inter-specific variation in the “scaly” group (a group of species with striking scale-like surface sculpture). The present study on the “non-scaly” Georissa is the continuation of the species revision for the genus. The “non-scaly” species are also diverse in shell sculptures. This informal group comprises Georissa with subtle spiral and/or radial sculpture. The combination of detailed conchological assessment and molecular analyses provides clear distinctions for each of the species. Conchological, molecular, and biogeographic details are presented for 16 species of “non-scaly” Georissa. Three of these are new to science, namely Georissacorrugatasp. n., Georissainsulaesp. n., and Georissatrusmadisp. n.

Highlights

The genus Georissa Blanford, 1864 (Hydrocenidae) comprises minute terrestrial snails, generally characterized by a small, dextral, conical, calcareous shell with ca. three teleoconch whorls (Bandel 2008; Thompson and Dance 1983; Vermeulen et al 2015)
We find there is no association based on colouration of G. borneensis with G. pyrrhoderma and the “williamsi”
Saul (1966) in her note on “Shell collecting in the limestone cave of Borneo” mentioned that during her trip to Lahad Datu, Sabah, they collected G. williamsi

Summary

Introduction

The genus Georissa Blanford, 1864 (Hydrocenidae) comprises minute terrestrial snails, generally characterized by a small, dextral, conical, calcareous shell with ca. three teleoconch whorls (Bandel 2008; Thompson and Dance 1983; Vermeulen et al 2015). Georissa is primarily restricted to environments rich in calcium carbonate (CaCO3) They are found in variable abundances on wet and shaded limestone walls or rocks, but occasionally on sandstone rocks and in vegetation that is not associated with a rocky substrate (Haase and Schilthuizen 2007; Khalik et al 2018). Striking allopatric patterns are well-known from several other microsnail taxa of Southeast Asia (see Liew et al 2014, Hoekstra and Schilthuizen 2011, Rundell 2008, Tongkerd et al 2004) These studies have led to the realisation that the geographic variation of different populations needs to be well understood and used as an important guideline for species delimitation. Such paraphyletic patterns are not unexpected when microgeographic speciation yields recently evolved; locally endemic species branched off from more widespread ancestors (Schilthuizen and Gittenberger 1996)

Methods

Results

Conclusion