Onchidiidae


Onchidiidae are a family of small, air-breathing sea slugs. They are shell-less marine pulmonate gastropod molluscs. Onchidiidae is the only family within the superfamily Onchidioidea.
These animals are quite unusual in that they are emphatically not opisthobranchs with gills, as are almost all of the sea slugs. Instead these creatures are pulmonates. They are more closely related to air-breathing land and freshwater snails and slugs than they are to most other sea snails and sea slugs.
This family has no subfamilies.
143 species names were created within the Onchidiidae, but until recently few species could be identified. In the late 1920s Hoffmann revised the family, and classified the described species into genera. Labbé later continued the revision and named many new genera in his classification of onchidiid slugs. Labbé also made mistakes in describing the anatomy of some species, and the Onchidiidae was not revised again for over 80 years. Finally, in 2016, the genus Onchidium was revised based on natural history, comparative anatomy, and DNA sequences. This was followed by a revision of the genus Onchidina, and the descriptions of onchidiid species in several new genera.

Anatomy

Adult onchidiids lack a shell, although a shell and operculum is present at the larval stage. The mantle cavity is reduced to the point of absence, correlating with a loss of gills, raphes, and other characters usually found in the mantle cavity. The organism is completely detorted.
Slugs in this family make and use love darts made of chitin.

Genetics

In this family, the number of haploid chromosomes lies between 16 and 20.

Habitat

Most of the species in this family are marine and are found in the intertidal zone. Many species live on rocky coasts, while others live in mangrove forests which may be marine or brackish. Onchidium stuxbergi was previously described as being collected from fresh water, but recent research has shown that the species has only been collected from brackish water.
Remarkably, some onchidiid species are completely terrestrial. Semperoncis montana and Platevindex ponsonbyi are the only known terrestrial species in the Onchidiidae. They live in high-elevation rainforests in Borneo and the Philippines.

Life habits

All these slugs breathe air. The marine ones breathe and move around and feed during low tide, when the water recedes and the slugs are exposed to the air.

Genera

Genera in the family Onchidiidae include:
;Synonymized genera :