Malacological Society of Australasia

Molluscan Research

Volume 19, Issue 2: 19 November 1998

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

David S. Brown

Department of Zoology, The Natural History Museum, Cromwell Road, London SW7 5BD.

The classification of freshwater snails belonging to the genus Gyraulus (Basommatophora: Planorbidae) from Tasmania is revised according to morphological observations on type materials, other shells collected in the 19thC, and about 920 alcohol-preserved specimens from 17 localities and mostly collected during the last 30 years. Four species-group taxa (atkinsoni, meridionalis, scottianus, tasmanicus) have previously been named from shells collected in Tasmania; two of these are type species for genera named by Iredale (1943) (meridionalis for Plananisus, scottianus for Pygmanisus). The present observations on the shell and body (pigmentation, kidney, intestinal loop and genital organs) suggest that there are two widely distributed species, G. meridionalis (including tasmanicus as a synonym) and G. scottianus. Lectotype material for G. meridionalis is designated here, from Circular Head, Tasmania. Although G. atkinsoni may be a conspecific form of meridionalis, it is maintained here as a distinct species in order to encourage further study of this depressed and sharply keeled form of shell. Descriptions are given of G. mienanus sp. n. from Great Lake and Gyraulus sp., another lacustrine form and possibly a distinct species, found in Lake Sorell. These two lacustrine taxa, and also G. meridionalis and G. atkinsoni are placed in Gyraulus sensu stricto, though with some doubt as in this group of Tasmanian taxa the position of attachment of the penis within the penis sheath differs from that previously known in this subgenus. If this difference should prove sufficient to define a new subgenus, its name could be Plananisus Iredale, 1943. Differences between G. scottianus and other Australian species, in the shell, kidney and penial structure, are sufficient to rank Pygmanisus Iredale as a subgenus. However, this taxon appears closely similar to G. (Torquis) of N America, Europe and western central Asia, suggesting the possibility that it has been introduced into Australia since European settlement. Further investigations are needed to determine the relationships between the Gyraulus faunas of Tasmania and mainland Australia. To achieve fuller understanding of Gyraulus in Australia, morphological data need to be supplemented by molecular genetics and ecological studies.
Key words: Planorbidae, Gyraulus, freshwater snail, taxonomy, Australia, Tasmania.

pp. 105-154.