Freshwater snails of the genus Gyraulus (Planorbidae) in Australia: taxa of the mainland

Abstract

Species of Gyraulus (Basommatophora: Planorbidae) are among the most widely distributed and abundant of freshwater snails in Australia Twenty species-group taxa have been described previously from shells collected on the Australian mainland, of which G. ordessus (Iredale) is the type species of Glyptanisus Iredale, 1943. In addition 3 species described from Tasmanian materials have been reported from the south-eastern mainland. Taxa found in mainland Australia are here revised according to morphological observations on type materials, other empty shells collected during the 19thC and early 20thC, and about 8300 alcohol-preserved whole snails from 258 localities, mostly collected during the last 30 years. lllustrations are provided here for the first time for 8 species-group taxa named by Iredale (1943): hesperus, idenus, leonatus, metaurus, ordesus, pelorius, speranus and stabilis. Observations on the shell and body (pigmentation, kidney, intestinal loop and genital organs) suggest that the previously reported Gyraulus fauna of mainland Australia may represent no more than 7 valid species, 6 of Gyraulus sensu stricto and 1 of Gyraulus (Pygmanisus). A third subgenus, G. (Plananisus) Iredale, 1943, should perhaps be recognised for G. meridionalis, currently placed in Gyraulus s.s., but which has a distinctive form of copulatory organ. Since G. ordessus is treated as a junior synonym of G. (G.) waterhousei, lredale's Glyptanisus is a synonym of ,Gyraulus s.s. Additions made here to the Australian fauna are G. edgbastonensis sp. n., known only from a few artesian springs in western Queensland, and G. chinensis Dunker, 1848, for which the present record in eastern South Australia probably results from introduction through human agency. The presence in south-eastern mainland Australia of species that live also in Tasmania was confirmed by examination of soft parts. G. meridionalis (syn. tasmanicus) is present in southern Victoria and eastern South Australia, but seems to be much less widely distributed than reported previously on the basis of identification from the shell alone. G. (Pygmanisus) scottianus (including as synonyms the mainland taxa leonatus and pelorius) is a little more widespread, extending into southern Queensland. During development of the penis in Australian species of Gyraulus s.s., the cellular lining of the distal end of the penis sheath apparently contributes material for the chitinisation of the penial stylet. Zoogeographical relationships of the Australian fauna of Gyraulus appear to lie entirely with SE Asia, though the distinctiveness of the Australian fauna, especially in the soft parts, suggests a long history of independent evolution. Since all indigenous Australian taxa have non-patchy mantle pigmentation, whereas all SE Asian taxa are patchy, it would seem that the non-patchy characterstate appeared early in the ancestry of the Australian fauna, preceding the development of other distinctive anatomical characters. Morphological data should be supplemented by molecular analysis, in order to improve understanding of species-boundaries within Gyraulus s. s. in Australia and to clarify relationships with the species of SE Asia.