Symposium 1 - Refining Molluscan Charactures

This symposium showed how molecular biology has taken an integral role alongside the traditional methods. In the keynote talk, Gerhard Haszprunar (Munich) asked "What is a good character?" Gastropod cephalic tentacles, like any 'good' systematic character define certain clades, but also have a functional role. They are present in nearly all gastropods, and are one of the few characters unaffected by torsion. Some differences occur in subclasses, often associated with senses, and these sensory structures may also define some clades.

Tim Collins (Florida, Miami) et al. used morphology, palaeontology and molecular biology as independent checks on one another in determining rates of evolution of the 18S rRNA gene in caenogastropods: violet snails, Ianthina, are so similar to wendletraps, Epitonium, that they are probably a late divergence rather than an ancient sister group. Charles Lydeard (Alabama) suggested that the `morphology ' of the 16S rRNA gene might contain useful phylogenetic data. Diarmid Ó Foighil (Michigan) used mtDNA and allozymes to reveal a strong geographical structure in the cosmopolitan rocky shore bivalve Lasaea, with perhaps four origins of polyploid clonal lineages. Ellen Strong (George Washington University) won an AMU student award for her discussion of inapplicable characters in systematics, including in her analysis original data on mid-gut characters. Winston Ponder (Australian Museum, Sydney) showed that the simple mouths of most caenogastropods and lower heterobranchs lack an introvert and resemble juvenile archaeogastropods, suggesting a paedomorphic origin. Kurt Schaefer (Vienna) described the fine structure of the adoral sense organ of protobranchs, and Gerhard Steiner (Vienna) revealed the paucity of data on species and characters in scaphopods. Roger Croll (Dalhousie) described the conservative evolution of gastropod giant neurones identifiable by their size, position, colour, connections, discharge pattern and transmitter type. Some can be traced between opisthobranchs and pulmonates (prosobranchs don't have identifiable neurones), and even, perhaps, between gastropod and bivalve larvae. John Taylor (Natural History Museum, London) described work with Yuri Kantor on the maturation of 'wishbone' marginal teeth in turrids - initially as a flat plate with later thickening and rolling of the edges. Conid hypodermic teeth form in a similar way, and have arisen by six independent routes.