Onchidiidae are a family of small, air-breathing sea (and land)
slugs. They are shell-less
marine (except for 2 species)[2]pulmonategastropodmolluscs. 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.
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species names were created within the Onchidiidae,[2] but until recently few species could be identified. In the late 1920s Hoffmann revised the family (based on the descriptions), and classified the described species into genera.[3] Labbé later continued the revision and named many new genera in his classification of onchidiid slugs.[4] Labbé also made mistakes in describing the anatomy of some species,[5] and the Onchidiidae was not revised again for over 80 years. The genus Onchidium was revised in 2016 based on natural history, comparative anatomy, and DNA sequences.[6] This was followed by revisions of the other onchidiid genera[7][8][9][10], and the descriptions of onchidiid species in several new genera.[5][11][12][13][14][15]
Anatomy
Adult onchidiids lack a shell, although a shell[16] 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.[17]
In this family, the number of
haploidchromosomes lies between 16 and 20 (according to the values in this table).[19]
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.[6]Onchidium stuxbergi (as E. ajuthiae, synonym in literature) was previously considered to be a fresh water species, but the species is now recognized to be found in brackish water habitats.[6]
Remarkably, some onchidiid species are completely terrestrial.[20]Semperoncis montana (synonym in literature: Platevindex apoikistes and Semperella montana) and Platevindex ponsonbyi are the only known terrestrial species in the Onchidiidae.[2] They live in high-elevation rainforests in
Borneo and the
Philippines.[2]
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.
^
abcdDayrat B. (2009). "Review of the current knowledge of the systematics of Onchidiidae (Mollusca: Gastropoda: Pulmonata) with a checklist of nominal species". Zootaxa. 2068: 1–26.
doi:
10.11646/zootaxa.2068.1.1.
S2CID4821033.,
preview.
^Hoffmann, H. (1928). "Zur Kenntnis der Oncidiiden". Zoologische Jahrbücher(Jena). 55: 29–118.
^Labbé, A. (1934). "Les Silicodermés (Labbé) du Museum d'Histoire Naturelle de Paris. Première partie: Classification, formes nouvelles ou peu connues". Annales de l'Institut Océanographique de Monaco. 14: 73–246.
^
abcdDayrat, Benoît; Goulding, Tricia C. (29 June 2017). "Systematics of the onchidiid slug Onchidina australis (Mollusca: Gastropoda: Pulmonata)". Archiv für Molluskenkunde. 146: 121–133.
doi:
10.1127/arch.moll/146/121-133.
^
abGoulding, Tricia; Khalil, Munawar; Tan, Shau Hwai; Dayrat, Benoit (2018). "A new genus and a new species of onchidiid slugs from eastern Indonesia (Gastropoda: Euthyneura: Onchidiidae)". Raffles Bulletin of Zoology. 66: 337–349.
^
abDayrat, Benoît; Goulding, Tricia C.; Apte, Deepak; Bhave, Vishal; Ngô Xuân, Quảng (27 July 2017). "A new genus and four new species of onchidiid slugs from South-East Asia (Mollusca: Gastropoda: Pulmonata: Onchidiidae)". Journal of Natural History. 51 (31–32): 1851–1897.
doi:
10.1080/00222933.2017.1347297.
ISSN0022-2933.
S2CID91153309.
^Dayrat, B.; Goulding T.C.; Khalil, M.; Lozouet, P., Tan, S.H. (2018) Systematic revision one clade at a time: A new genus of onchidiid slugs from the Indo-West Pacific (Gastropoda: Euthyneura: Onchidiidae). Raffles Bulletin of Zoology 66: 814–837.
^Barker G. M.: Gastropods on Land: Phylogeny, Diversity and Adaptive Morphology. in Barker G. M. (ed.): The biology of terrestrial molluscs. CABI Publishing, Oxon, UK, 2001,
ISBN0-85199-318-4. 1–146, cited pages: 139 and 142.