New mollusc research answers major relationship question

A team of biologists including Dr Nerida Wilson from the Australian Museum has resolved one of the enduring questions in understanding relationships within the ‘family tree’ of molluscs – the second largest group of animals on earth.

Molluscs include bivalves (oysters, scallops, clams), gastropods (snails, limpets, slugs), chitons, cephalopods (squid, octopus, cuttlefish, Nautilus) and monoplacophorans (shelled limpet-like creatures living in very deep water).

Monoplacophorans are often referred to as ‘living fossils’, as they were once diverse but thought to have gone extinct 375 million years ago until the amazing discovery of live animals in the 1950s. These animals showed strange features that had not changed dramatically through time, and were then thought to represent primitive molluscs.

Speculation - even controversy – subsequently ensued over their evolutionary relationship to other molluscs.

In a work published in Nature magazine (15/12/2011), Dr Wilson and her colleagues have assembled the most extensive and comprehensive molluscan DNA data set to date, analyzing 1185 regions of the genome (hundreds of genes) to clarify the molluscan family tree.

This is the first time that such phylogenomic research has included a member of the Monoplacophora.

The results of this research demonstrate a link between the enigmatic monoplacophorans and cephalopods, considered to be a highly sophisticated group of molluscs because of their swimming abilities, visual acuity and intelligence. This new classification is the latest extension to a body of knowledge about molluscan evolution, which had been relatively static until the emergence of new studies in the last 10 years.

Resolving the evolutionary relationships of molluscs with phylogenomic tools
Smith, S A, Wilson, N G, Goetz, F, Feehery, C, Andrade S CA , Rouse, G W, Giribet, G, Dunn, C W