Re: Monophyly of Opisthobranchs

October 26, 2002
From: Lucas Cervera

Hi Bill,
I'm attaching an abstract of a very recent paper resulting from a project in which I'm involved. In this paper, we support the monophyly of the opisthobranchs on the basis on a synapomorphy of the mitochondrial genome. Hopefully this will be of interest for all our colleagues who are interested in the phylogeny of opisthobranchs and gastropods. Since Mikkelsen (1996) proposed that some cephalaspidean groups (for example, Acteonidae) were more related to "prosobranch" groups than to the rest of cephalaspideans and opisthobranchs in general, other cladistic analyses have reached similar conclusions, which are not supported by our studies.

Since the paper has been published in a non malacological journal I thought the Sea Slug Forum would be a good way to bring it to their attention

Grande, C., Templado, J, Cervera, J.L. & Zardoya, R. (2002) The Complete Mitochondrial Genome of the Nudibranch Roboastra europaea (Mollusca: Gastropoda) Supports the Monophyly of Opisthobranchs. Molecular Biology and Evolution, 19:1672-1685.

The complete nucleotide sequence (14,472 bp) of the mitochondrial genome of the nudibranch Roboastra europaea (Gastropoda: Opisthobranchia) was determined. This highly compact mitochondrial genome is nearly identical in gene organization to that found in opisthobranchs and pulmonates (Euthyneura) but not to that in prosobranchs (a paraphyletic group including the most basal lineages of gastropods). The newly determined mitochondrial genome differs only in the relative position of the trnC gene when compared with the mitochondrial genome of Pupa strigosa, the only opisthobranch mitochondrial genome sequenced so far. Pupa and Roboastra represent the most basal and derived lineages of opisthobranchs, respectively, and their mitochondrial genomes are more similar in sequence when compared with those of pulmonates. All phylogenetic analyses (maximum parsimony, minimum evolution, maximum likelihood, and Bayesian) based on the deduced amino acid sequences of all mitochondrial protein-coding genes supported the monophyly of opisthobranchs. These results are in agreement with the classical view that recognizes Opisthobranchia as a natural group and contradict recent phylogenetic studies of the group based on shorter sequence data sets. The monophyly of opisthobranchs was further confirmed when a fragment of 2,500 nucleotides including the mitochondrial cox1, rrnL, nad6, and nad5 genes was analyzed in several species representing five different orders of opisthobranchs with all common methods of phylogenetic inference. Within opisthobranchs, the polyphyly of cephalaspideans and the monophyly of nudibranchs were recovered. The evolution of mitochondrial tRNA rearrangements was analyzed using the cox1+rrnL+nad6+nad5 gene phylogeny. The relative position of the trnP gene between the trnA and nad6 genes was found to be a synapomorphy of opisthobranchs that supports their monophyly.

Best wishes,

Cervera, L., 2002 (Oct 26) Re: Monophyly of Opisthobranchs . [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Lucas,
Thanks for drawing our attention to this interesting study.
Bill Rudman