Onychopoda

Onychopoda are a specialised order of branchiopod crustaceans, belonging to the superorder Cladocera.

Onychopoda
Evadne spinifera
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Branchiopoda
Superorder:	Diplostraca
Order:	Onychopoda Sars, 1865 [1]
Families
Cercopagididae Mordukhai-Boltovskoi, 1968 Podonidae Mordukhai-Boltovskoi, 1968 Polyphemidae Baird, 1845

The order Onychopoda is "one of the most morphologically distinctive groups of cladocerans".^[2] They have only four pairs of legs, compared to five or six pairs in Ctenopoda and Anomopoda.^[3] Unusually among branchiopod crustaceans, Onychopoda share with Haplopoda the presence of segmented appendages, which are used for grasping prey.^[4]

Most species of Onychopoda live in the waters of the Ponto-Caspian basin (Caspian Sea, Aral Sea, Black Sea including Sea of Azov), in remnants of the ancient Paratethys ocean.^[5] Some other species live in fresh water or in the oceans, where they can be widespread.^[5]

There are three families, containing 10 genera and around 33 described species, most of which are endemic to the Ponto-Caspian basin:^[2]

• Cercopagididae Mordukhai-Boltovskoi, 1968 – 2 genera (Cercopagis and Bythotrephes), 14 species; Black Sea & Caspian Sea
• Podonidae Mordukhai-Boltovskoi, 1968 – 7 genera, 17 species; Pont-Caspian (Caspievadne, Cornigerius and Podonevadne) and marine (Evadne, Pleopis, Podon and Pseudevadne)
• Polyphemidae Baird, 1845 – 1 genus (Polyphemus), 2 species; fresh water

The embryos are protected by a brood pouch, which also secretes nutrients to aid their development. This may be related to the colonisation of the oceans, since the only other marine cladoceran, Penilia avirostris, has a similar pouch as a result of convergent evolution.^[2]

See also

• Crustaceans portal
• Arthropods portal

• Bythotrephes longimanus
• Cercopagis pengoi

References

1. J. W. Martin & G. E. Davis (2001). An Updated Classification of the Recent Crustacea (PDF). Natural History Museum of Los Angeles County. pp. 1–132.
2. M. E. A. Cristescu & P. D. N. Hebert (2002). "Phylogeny and adaptive radiation in the Onychopoda (Crustacea, Cladocera): evidence from multiple gene sequences" (PDF). Journal of Evolutionary Biology. 15 (5): 838–849. doi:10.1046/j.1420-9101.2002.00466.x.
3. D. R. Khanna (2004). "Segmentation in arthropods". Biology of Arthropoda. Discovery Publishing House. pp. 316–394. ISBN 978-81-7141-897-8.
4. G. Fryer (1998). "A defence of arthropod polyphyly". In Richard A. Fortey; Richard H. Thomas (eds.). Arthropod Relationships. Volume 55 of Systematics Association Series. Springer. pp. 23–34. ISBN 978-0-412-75420-3.
5. Stefan Richter; Anke Braband; Nikolai Aladin; Gerhard Scholtz (2001). "The phylogenetic relationships of "predatory water-fleas" (Cladocera: Onychopoda, Haplopoda) inferred from 12S rDNA". Molecular Phylogenetics and Evolution. 19 (1): 105–113. doi:10.1006/mpev.2000.0901. PMID 11286495.

External links

• Podon sp. fact sheet - Guide to the marine zooplankton of south eastern Australia
• Evadne sp. fact sheet - Guide to the marine zooplankton of south eastern Australia