The interesting little Rhodope veranyii, which has no odontophore, has been associated by systematists both with these simplified Opisthobranchs and with Rhabdocoel Planarians.
For a comparison of various Opisthobranchs, Aplysia will be found to present a convenient starting-point.
It is one of the more typical Opisthobranchs, that is to say, it belongs to the section Tectibranchia, but other members of the suborder, namely, Bulla and Actaeon (figs.
The great development of the parapodia seen in Aplysia is usual in Tectibranchiate Opisthobranchs.
The typical character is retained by the heart, pericardium, and the communicating nephridium or renal organ in all Opisthobranchs.