Onychopoda

From Wikipedia, the free encyclopedia

Onychopoda

Evadne spinifera

Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Crustacea
Class:	Branchiopoda
Infraclass:	Diplostraca
Order:	Cladocera
Suborder:	Onychopoda Sars, 1865 ^[1]

Families

Cercopagididae Mordukhai-Boltovskoi, 1968
Podonidae Mordukhai-Boltovskoi, 1968
Polyphemidae Baird, 1845

Onychopoda are a specialized order of branchiopod crustaceans formerly included in the order Cladocera. The body is up to about 12 mm (0.5 in) in length, but much of the length of the longest species is made up by a caudal process.

The head and thorax are short, as is the abdomen in some species, but in others it is drawn out into a long caudal process. A carapace is present but is reduced to a dorsal brood pouch, leaving the body naked. A large median compound eye occupies much of the head.

Onychopods swim actively by means of their antennae—the antennules are small and sensory—and seize their food with their four pairs of grasping trunk limbs. Most are predators, but detritus is also eaten by some species. The mandibles are stoutly denticulate.

Reproduction is mostly by parthenogenesis (males are unknown in some species from the Caspian Sea); eggs and young are carried in the brood pouch. Sexual reproduction gives rise to freely shed resistant eggs that overwinter in temperate zone species. Onychopods occur in the sea and fresh water and are worldwide in distribution, but fresh-water species occur only in the Holarctic temperate zone. There is a remarkable group of endemic species in the Ponto-Caspian region.