Notaspidea
The notaspids are primitive opisthobranchs that have a typical molluscan ctenidium rather than a pseudobranch (a "false" secondarily derived respiratory structure). The Pleurobranchidae lack an external shell, or are devoid of a shell altogether.
Some notaspid opisthobranchs have lost their shells (e.g., the preceding species), and others (family Umbraculidae), such as this one, have retained their limpet-shaped shells.
Glossary
- bilateral symmetry
-
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
- ectothermic
-
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature