Onchidiidae

Onchidiidae
Onchidella sp.
Onchidella nigricans
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Gastropoda
(unranked):	clade Heterobranchia clade Euthyneura clade Panpulmonata clade Eupulmonata clade Systellommatophora
Superfamily:	Onchidioidea Rafinesque, 1815
Family:	Onchidiidae Rafinesque, 1815[1]
Genera
See text
Synonyms
Peroniidae Keferstein, 1865 Onchidellidae Labbé, 1934 Scaphidae Labbé, 1934 Hoffmannolidae Starobogatov, 1976 Onchidinidae Starobogatov, 1976 Peroninidae Starobogatov, 1976 Platevindecidae Starobogatov, 1976 Quoyellidae Starobogatov, 1976

Onchidiidae are a family of small, air-breathing sea (and land) slugs. They are shell-less marine (except of 5 species)^[2] 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 slug^{[disambiguation needed ]}s. 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 (according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005).

There are 143 species names within the Onchidiidae,^[2] but a detailed revision has not been made yet,^[2] because there is no living malacologist expert who can properly identify them.^[2]

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.^[3]

Slugs in this family make and use love darts made of chitin.^[4]

Genetics

In this family, the number of haploid chromosomes lies between 16 and 20 (according to the values in this table).^[5]

Habitat

Most of the species in this family are marine and are found in the intertidal zone on rocky coasts. However two species live in brackish water and three are terrestrial.

Onchidium typhae (India) and Labbella ajuthiae (synonym named in literature : Elophilus ajuthiae) (Thailand) are the only two species in the Onchidiidae that live in brackish water.^[2] They can also live in freshwater.^[2]

Oncis ponsonbyi (synonym named in literature : Platevindex ponsonbyi) and Semperoncis montana (synonym named in literature : Platevindex apoikistes and Semperella montana) are the only two 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.

Genera

Genera in the family Onchidiidae include:^[6]

• Buchanania Lesson, 1831
• Hoffmannola Strand, 1932
• Labbella Starobogatov, 1976
• Lessonina Starobogatov, 1976
• Onchidella Gray, 1850^[7]
• Onchidina Semper, 1885
• Onchidium Buchanan, 1800 - type genus
• Onchis Férussac, 1821
• Paraoncidium Labbé, 1934
• Paraperonia Labbé, 1934
• Peronia Fleming, 1822
• Peronina Plate, 1893
• Quoya Labbé, 1934
• Scaphis Labbé, 1934
• Semperoncis Starobogatov, 1976

Synonymized genera 

• Arctonchis Dall, 1910 : synonym of Onchidella J. E. Gray, 1850
• Elophilus Labbé, 1935 : synonym of Labbella Starobogatov, 1970
• Eudrastus Gistel, 1848 : synonym of Peronia Fleming, 1822
• Occidentella Hoffmann, 1929 : synonym of Onchidella J. E. Gray, 1850
• Peroniella Starobogatov, 1976  : synonym of Onchidella J. E. Gray, 1850
• Platevindex Baker, 1938 : synonym of Oncis Plate, 1893
• Quoyella Starobogatov, 1976 : synonym of Quoya Labbé, 1934
• Semperella Labbé, 1934 : synonym of Semperoncis

References

1. ^ Rafinesque C. S. (1815). Analyse de la nature ou tableau de l'univers et des corps organisés. Palerme, 223 pp., page 142.
2. ^ ^{a b c d e f g h} Dayrat 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. , preview.
3. ^ Morton, Brian (1992). The Marine Flora and Fauna of Hong Kong and Southern China III___ Fouling and pollution, morphology, behavious and physiology, Hoi Ha Wan. Hong Kong University Press. ISBN 9789622092952. http://books.google.com/?id=hbqVv5r3FgsC&pg=PA719. 
4. ^ Chung D. J. D.: Molluscan 'Love darts'? Hawaiian Shell News, 1986 May, Vol 34(5), pages 3-4. http://s190418054.onlinehome.us/HSN/1980/8605.pdf
5. ^ 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, ISBN 0-85199-318-4. 1-146, cited pages: 139 and 142.
6. ^ World Register of Marine Species : Onchidiidae; accessed 13 September 2010 (with modifications).
7. ^ "Onchidella". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=78761. , accessed 13 September 2010.

Further reading

• Britton K. M. (1984). "The Onchidiacea (Gastropoda, Pulmonata) of Hong Kong with a worldwide review of the genera". Journal of Molluscan Studies 50 (3): 179–191.  abstract.

External links

• Onchidiidae at National Center for Biotechnology Information (NCBI) website.