Systematics or Phylogenetics
Evolution and systematics of invertebrates is currently widely studied. However, results of different studies are often controversial, and it is hard to obtain answers from hypothesis in this domain, even more when fossil records are scarce (Gosliner 1981; Gosliner & Ghiselin 1984).
Vonnemann et al. (2004) tried reconstruct the phylogeny of the opisthobranchia by means of
18s and 28s rRNA gene sequences. Unfortunately, this study gave raise to new hypothesis about the relationships between groups. As a matter of fact, the phylogeny of the Opisthobranchia is still unresolved,
both in respect of the origin of the whole group as well as of the interrelationships of its major clades.
Figure: Example of phylogenic tree obtained through analysis of 18s and 28s rRNA gene sequence (Vonnemann et al. 2004)
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