Phylogeny of the Opisthobranchia
The evolutionary relationships of the opisthobranchs to each other and to other gastropod molluscs is an area which has always generated much discussion. In the past decade the use of new computer-based techniques, such as cladistics, and the use of new characters such as DNA analysis, have generated new and interesting ideas. This is definitely a 'work in progress' so there are, at present, no final answers. Here are a few important references. Please let me know if I have missed any significant ones, or you know of a new one I have not included.
• Gosliner, T.M. & Ghiselin, M.T. (1984) Parallel evolution in opisthobranch gastropods and its implications for phylogenetic methodology. Systematic Zoology, 33(3): 255-274.
• 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.
• Mikkelsen, P.M. (1996) The Evolutionary Relationships of Cephalaspidea S.L. (Gastropoda: Opisthobranchia): A Phylogenetic Analysis. Malacologia, 37(2): 375-442.
• Thollesson, M. (1999) Phylogenetic analysis of dorid nudibranchs (Gastropoda: Doridacea) using the mitochondrial 16s rRNA gene. J. Moll. Stud. 65: 335-353.
• Medina, M, & Walsh, P.J. (2000) Molecular Systematics of the Order Anaspidea based on mitochondrial DNA Sequence (12S, 16S, and COI). Molecular Phylogenetics and Evolution, 15(1), 41-58.
Rudman, W.B., 2002 (October 24) Phylogeny of the Opisthobranchia. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/slugroots