Family PLANORBIDAE

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Family PLANORBIDAE

Compiler and date details

Brian J. Smith, Queen Victoria Museum, Launceston Shannon Reid and Winston F. Ponder, Australian Museum, Sydney

Introduction

The Planorbidae are the largest and the most diverse family of freshwater pulmonate snails and has a worldwide distribution. In Australia it is represented by a wide variety of taxa and is often the only group of freshwater molluscs found in many areas. Planorbiids are confined to waters of low salinity and are usually associated with macrophytes and algae on which they feed.

Many names have been given to members of the Planorbidae, largely based on shell shape and form, especially the high-spired taxa. More comprehensive collecting suggests that many of the shell forms are ecomorphs—local varieties associated with particular environmental conditions, but this has not been properly demostrated in most cases. A taxonomic revision using comparative anatomy of the flat-spired taxa, was undertaken by Brown (1981, 1998, 2001) but a revision of the high-spired groups using anatomy and molecular data is long overdue. While the high-spired genera have been reviewed by Walker (1988), the species based classification described below must be considered as very tentative, pending revisionary work. Many of the available names have been listed under incertae sedis, pending proper assessment.

The Planorbidae are characterized by having a sinistal animal with a simple (ie non-digitate) mantle, an external secondary gill (pseudobranch) and lack of operculum. The shells are sinistral and are either high-spired, planispiral or a limpet- like with a minute, coiled apex.

Members of the freshwater limpet family Ancylidae, found worldwide, are now placed in the Planorbidae. They form only a small component of the freshwater fauna of Australia — Ferrissa (Pettancylus) petterdi, Ferrissa (Pettancylus) tasmanicus and Stimulator consetti have been recorded. The species are confined to non-saline waters, but are found in a wide range of habitats from stagnant pools to fast flowing creeks and rivers. The shell is small and patelliform without coiling and with a backward- pointing apex. The foot is enlarged to enable the limpet to cling tightly to the substratum. The animal is sinistral and a small pseudobranch is present. The Australian members were reviewed superficially by Hubendick (1967). Zilch (1959) used the family name Ferrissiidae. The arrangement followed below certainly requires revision.