The opisthobranchs (subclass Opisthobranchia) are mollusks (phylum Mollusca) and gastropods (class Gastropoda), a group comprising more than 3000 species globally, almost all marine, with a fascinating variety of shapes and colors.
Popularly known as “sea slugs”, the opisthobranchs have only caught the attention of a handful of naturalists in recent centuries, but recently its popularity has grown thanks to scuba diving, although the size (ranging from some millimeters to a few inches) is often overlooked by those who do not seek them specifically.
Unlike marine snails (Prosobranchia), very popular among collectors of shells, these marine gastropods (in a certain way related to the snails we all know) have reduced their shell (in most cases absent in adult specimens) and paleal cavity and gill, have covered his shell with tegument to a greater or lesser degree, in many cases have developed parapods (lateral extensions of the foot, with different functionality) and Cerata (protrusions of the body with defensive functionality, etc.). changes that, in the end, give the animal an external bilateral symmetry not corresponding to the internal organization of the body.
The opisthobranchs are actually grouped into 11 groups:
- Suborder Acochlidiacea Odhner, 1937
- Suborder Thecosomata Blainville, 1824
- Suborder Gymnosomata Blainville, 1824
- Clade Allogastropoda (Lower Heterobranchia) Haszprunar, 1985
- Suborder Cephalaspidea P. Fischer, 1883
- Suborder Runcinacea Burn, 1963
- Suborder Sacoglossa von Ihering, 1876
- Suborder Anaspidea P. Fischer, 1883
- Suborder Pleurobranchomorpha Schmekel, 1985
- Suborder Umbraculida Odhner, 1939
- Suborder Nudibranchia Blainville, 1814
The suborder of nudibranchs (Nudibranchia) is probably the most popular.