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Cephalocarida
From Wikipedia, the free encyclopedia
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Chiltonella |
Cephalocarida is a class inside the subphylum Crustacea that comprises only about nine shrimp-like benthic species. They were discovered in 1955, and are commonly referred to as horseshoe shrimps. Although a second family, Lightiellidae, is sometimes used, all cephalocarids are generally considered to belong in just one family: Hutchinsoniellidae. Even though there is no fossil record of cephalocarids, most specialists believe them to be primitive among crustaceans.
The anatomy of cephalocarids is relatively simple, compared to that of other crustaceans. Their body is small (2 to 3.7 mm long) and elongate, comprising a head, an 8-segmented thorax with biramous appendages, and an 11-segmented abdomen which bears a telson but no other appendages. The second pair of maxillae closely resemble the appendages of the thorax. The eyes are very small and buried in the exoskeleton, which makes them appear eyeless.
Cephalocarids are found from the intertidal zone down to a depth of 1500 m, in all kinds of sediments. Cephalocarids feed on marine detritus. To bring in food particles, they generate currents with the thoracic appendages like the branchiopods and the malacostracans. Food particles are then passed anteriorly along a ventral groove, leading to the mouthparts.