Evolution & Systematics

Molecular phylogenetic analyses suggest that Sacoglossa is a monophyletic group, with Pulmonata being the sister group (Maeda et al. 2010). As members of Pulmonata lack uniserial radula, this characteristic has been labelled a synapomorphy of Sacoglossans, and it is used in suctorial feeding of algae prey. If Sacoglossa and Pulmonata are considered monophyletic sister groups, Opisthobranchia would then be considered a paraphyletic group, and future taxonomic rearrangements of Sacoglossa, Pulmonata and Opisthobranchia may be required (Maeda et al. 2010). 

There are several synapomorphies which separate Elysiidae from other Sacoglossa, such as parapodia containing disgestive gland tubules, a highly branched prostrate gland and ampulla separated from the hermaphroditic duct (Jensen 1992).