Hypselostoma Benson, 1856

Genus Hypselostoma Benson, 1856

Hypselostoma Benson, 1856 b: 342 View in CoL (replacement name for Tanystoma Benson, 1856 View in CoL , non Motschulsky 1845, Carabidae View in CoL , Coleoptera ).

Gyliotrachela Tomlin, 1930: 24. (replacement name for Gyliauchen Pilsbry 1917 non Nicoll 1915, Platyhelminthes, Trematoda) syn. nov. View in CoL

Antroapiculus Panha & Burch, 2002 a: 144–148 View in CoL . syn. nov.

Diagnosis.

This genus is subdivided into four species groups: i) H. bensonianum group ii) H. hungerfordianum group; iii) H. terae group and iv) H. tubiferum group. This subdivision is based on the shell surface sculpture (coupled with apertural barrier morphology and geographic distribution in H. terae group) which is raised spirally striated in H. bensonianum group, granulated (sandpaper-like) in H. hungerfordianum group and fine, pasty in H. terae and H. tubiferum group. Most representatives share the depressed-conical or conical shell shape with last whorl adnate to or detached from the penultimate.

Remarks.

Hypselostoma aenigma sp. nov. is provisionally placed in this genus due to the specific apertural barrier arrangement. Hypselostoma torta sp. nov. is also not a typical representative since it has non-raised spiral striae which are probably not homologous to the raised ones as usual for the genus.

Genera Gyliotrachela and Antroapiculus are both treated as junior synonyms of Hypselostoma due to the following facts: i) Antroapiculus is described based on a unique shell (flat with strongly downwards descending aperture) and a single lamella on the parietal side (parietal lamella). This however does not seem to warrant separation of a new genus since the flat shell ( H. tridentatum , H. khaowongkot , H. utongense ) and strongly descending aperture ( H. srakeoense , H. chaunosalpinx , H. fungus sp. nov., H. transitans , H. torticollis ) are shared with other congeners. Furthermore, apertural barrier arrangement is also similar to H. torticollis , H. fungus sp. nov., H. depressum which indicates that the combination of characters in H. pendulum could just be an autapomorphic state which could be changed rapidly during the evolution; ii) Gyliotrachela is treated distinct from Hypselostoma solely based on the separated parietal and angular lamella on the parietal side (Pilsbry 1917). Since we have found several examples of species with almost exactly the same shell morphology, but with different apertural barrier arrangements (Fig. 262 View Figure 262 ), we find it less likely that they belong to different genera and find this criterium insufficient.

1. Hypselostoma bensonianum group

Diagnosis. Hypselostoma bensonianum group is characterised by raised and usually widely spaced spiral striation (in form of threads).

Remarks. A total of 46 species belong to this group. This group has a wide distribution across Southeast Asia as well as in Australia where only one species can be found. In Southeast Asia, this group spans from central and eastern Myanmar to Taiwan as well as southwards all the way to Indonesia. Northernmost localities on mainland Southeast Asia are known from Luang Prabang Province in Laos.