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Diastylis laevis.jpg
Diastylis laevis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Superorder: Peracarida
Order: Cumacea
Family: Diastylidae
Bate, 1856 [1]

Diastylidae is one of the eight most commonly recognised families of crustaceans of the order Cumacea. They are marine creatures especially common around the 30th parallel north.[2]


General body plan of diastylids, based on D. laevis

Diastylidae have a medium to large, free telson, that has not fused with the last pleon segment. The telson usually bears two terminal setae.[3]

Males have generally two pairs of pleopods, though in rare cases they may be rather small or even entirely absent. The flagellum of the second antenna reaches past the pereon.[3]

In females the second antenna is much smaller than the first antenna. In males the third maxilliped and the first four pereiopods almost always have exopods (outer branches). In females they may, in rare cases, be absent from all but the third maxillipeds, and the two first pereiopods.[3]

The interior branch of the uropods are generally made up of two or three segments, but in some rare case may have just one. Members of this family frequently show clear sexual dimorphism.[3]


There are around 285 species,[4] in 24 genera:[5]


  1. ^ C. Spence Bate (1856). "On the British Diastylidae". Annals and Magazine of Natural History. 2. 17 (102): 449–464. doi:10.1080/00222935608697553. 
  2. ^ L. Watling & L. D. McCann (1997). "Cumacea". In James A. Blake & Paul H. Scott. Taxonomic Atlas of the Benthic Fauna of the Santa Maria Basin and the Western Santa Barbara Channel, Volume 11: The Crustacea, Part 2: Isopoda Cumacea and Tanaidacea. Santa Barbara Museum of Natural History. pp. 121–180. ISBN 0-936494-16-6. 
  3. ^ a b c d N. S. Jones (1976). British Cumaceans. Synopses of the British Fauna (New Series) 7. London & New York: Academic Press. pp. 12–13. ISBN 978-0-12-389350-5. 
  4. ^ L. S. Watling; S. Gerken; et al. (2003). The Cumacea. DELTA database and INTKEY illustrated, interactive key to the crustacean order Cumacea. 
  5. ^ Les Watling (2011). L. Watling, ed. "Diastylidae". World Cumacea database. World Register of Marine Species. Retrieved March 26, 2011. 

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