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]
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]
^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. ISBN978-0-412-75420-3.