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Gastopod Phylogeny: Results
We have provided the first rigorous computer-based phylogenetic analysis of the gastropods using morphological characters (Ponder & Lindberg, 1996, 1997). This agrees with other recent conclusions based on morphology (Golikov & Starobogatov, 1975; Lindberg, 1988; Haszprunar, 1988), that gastropods fell into two main groups, were confirmed and we have named them - the Eogastropoda (including the true limpets or Patellogastropoda and their extinct coiled ancestors) and the Orthogastropoda - the rest of the gastropods. The previously accepted division of the gastropods into three subclasses - Prosobranchia, Opisthobranchia and Pulmonata, cannot be maintained.
Within the orthogastropods there are four main monophyletic groups (clades) [Vetigastropoda, Neritopsina, Caenogastropoda and Heterobranchia (Haszprunar 1985b, 1988; includes the pulmonates and opisthobranchs)] have, to a large extent, been identified in recent molecular and morphological studies, including our investigations. The positions of the hot-vent Neomphaloidea and the deepsea limpets of the Cocculinoidea are the only groups that were not well resolved in our analysis, mainly because of a lack of adequate data on ultrastructure.
Important findings include the conclusion that the very large clades Caenogastropoda and Heterobranchia (includes the pulmonate land snails and slugs), and the Opisthobranchia - (the seaslugs and their relatives)- are both paedomorphic and that the release from the constraints of ancestral adult morphologies played a major part in the evolution of these groups.
A large morphological data set is the basis of a preliminary analysis (Ponder & Lindberg, 1996) and a major review and analysis (Ponder & Lindberg, 1997). This latter paper described and reviewed 117 characters used in the analysis, and discussed the evolution and adaptive radiation of the gastropods. The data used are a combination of existing and new data, including new information on anatomy and shell structure (the latter from C. Hedegaard & D. Lindberg).
Molecular investigations of this project were based on a group of taxa representative of the major clades of gastropods. Sequencing efforts concentrated on two regions of the 28S rDNA towrds the 3' end of the gene (corresponding to bases 4261-4597 and 6400-6701 of the Drosophila melanogaster rDNA cistron in GENBANK entry DRORGAB) and the Histone H3 gene (corresponding to bases 1-351 of the chicken sequence (GENBANK entry CHKH3A). The paper resulting from this study is now in press (Colgan and Ponder, 2000).
References
Publications from this project
Other useful references
Gastropod Phylogeny page
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