| Cephalocarida | |
|---|---|
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| Hutchinsoniella macracantha | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Cephalocarida Sanders, 1955 |
| Order: | Brachypoda Birshteyn, 1960 |
| Family: | Hutchinsoniellidae Sanders, 1955 |
| Genera | |
| Synonyms | |
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TheCephalocarida, fromAncient Greek κεφαλή (kephalḗ), meaning "head", and καρίς (karís), meaning "shrimp", are aclass in thesubphylumCrustacea comprising only 12species. Both thenauplii and the adults arebenthic.[1] They were discovered in 1955 byHoward L. Sanders,[2] and are commonly referred to ashorseshoe shrimp. They have been grouped together with theRemipedia in theXenocarida. Although a secondfamily, Lightiellidae, is sometimes used, all cephalocaridans are generally considered to belong in just one family:Hutchinsoniellidae.Fossil records of cephalocaridans have been found in theOrdovicianCastle Bank site.[3]
These arehermaphroditic and pigmentless crustaceans with an elongated and translucent body that measures 2 to 4 mm (0.079 to 0.157 in) in length. A heart is present, and theirexopods and pseudepipodites appears to be used for gas exchange.[5][6] They have a large head, the hind edge of which covers the firstthoracic segment. The thorax consists of nine limb-bearing segments (thoracic limb VIII absent in Lightiella), followed by 10 limbless abdominal segments and atelson. In the larva, all the trunk segments are ring-shaped, but more dorsoventrally flattened than in the adults. During growth the anterior segments turns into the thorax and the posterior segments which makes up the abdomen remains ring-shaped.[7] No eyes have been observed in either the adult or larval stages, presumably because of their muddy natural habitat. The second pair ofantennae is located behind the mouth; in all other crustaceans the antennae are in front of the mouth at the adult stage, and only their larvae have antennae that have the same location as adult cephalocaridans.[8][9]
The mouth is located behind the large upper lip, flanked bymandibles. The first pair ofmaxillae is very small, and the second pair has the same structure as the following thoracic legs: a large basal part, equipped with outgrowths on the inner side, used in locomotion, a forked inner branch and two outer lobes - referred to as the "pseudoepipod" and the "exopod". The structural and functional similarity between the maxillae and the legs may be a sign of primitive organization; the maxillae are not specialized, as they are in other crustaceans.[8]
Cephalocaridans are found from theintertidal zone down to a depth of 1,500 m (4,900 ft), in all kinds ofsediments. Cephalocaridans feed on marinedetritus. To bring in food particles, they generate currents with the thoracic appendages like thebranchiopods and themalacostracans. Food particles are then passedanteriorly along aventral groove, leading to themouthparts.[10]
Data related toCephalocarida at Wikispecies