The Morphology, Taxonomy and Genetic-Structure of Tatea (Mollusca, Gastropoda, Hydrobiidae), Estuarine Snails From Temperate Australia

Abstract

The estuarine hydrobiid genus Tatea is found throughout temperate Australia. Two, often sympatric, species, T. rufilabris and T. huonensis are recognised, both ranging from southern Western Australia to southern Queensland. Whereas no single anatomical character differentiates the two species, they can be separated on their shell morphology; there are up to three fixed, or nearly fixed, differences among 16 loci between sympatric populations of the two species. Geographic variation in both phenotype (expressed in shell morphology) and genotype (allozymes) which is present in T. rufilabris is not great enough or sufficiently consistent to imply the presence of multiple cryptic species within this taxon. Genotypic differences do, however, suggest the possibility of subdivision of T. huonensis into eastern and southern populations. Investigation of salinity tolerances shows that the two species are euryhaline with a similar range of tolerance. The anatomy and egg capsules are described for the first time. Autapomorphies distinguishing Tatea from related Australasian genera include a protoconch indicating a free-swimming (lecithotrophic?) larval stage, a black pigment ring near the distal ends of the cephalic tentacles, and a female genital opening located beneath the middle of the capsule gland. A scenario is presented which may account for the apparent lack of speciation in estuarine animals in temperate Australia.