The Cephalocarida, from Ancient Greek κεφαλή ( kephalḗ), meaning "head", and καρίς ( karís), meaning "shrimp", are a class in the subphylum Crustacean comprising only 12 species. Both the nauplii and the adults are Benthic zone.[ Key for the identification of crustacean nauplii - GfBS] They were discovered in 1955 by Howard L. Sanders,[ Welsh fossils uncover an ancient 'marine dwarf world']
Taxonomy
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Class Cephalocarida Sanders 1955
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Order Brachypoda Birshteyn 1960
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Family Hutchinsoniellidae Sanders 1955
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Genus Chiltoniella Knox & Fenwick 1977
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Chiltoniella elongata Knox & Fenwick 1977
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Genus Hampsonellus Hessler & Wakabara 2000
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Hampsonellus brasiliensis Hessler & Wakabara 2000
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Genus Hutchinsoniella Sanders 1955
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Hutchinsoniella macracantha Sanders 1955
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Genus Lightiella Jones 1961
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Lightiella floridana McLaughlin 1976
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Lightiella incisa Gooding 1963
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Lightiella magdalenina Carcupino et al. 2006
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Lightiella monniotae Cals & Delamare Deboutteville 1970
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Lightiella serendipita Jones 1961
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Genus Sandersiella Shiino 1965
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Sandersiella acuminata Shiino 1965
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Sandersiella bathyalis Hessler & Sanders 1973
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Sandersiella calmani Hessler & Sanders 1973
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Sandersiella kikuchii Shimomura & Akiyama 2008
Description and anatomy
These are
Hermaphrodite and pigmentless crustaceans with an elongated and translucent body that measures in length. A heart is present, and their exopods and pseudepipodites appears to be used for gas exchange.
[ Class Cephalocarida Sanders, 19551 in - Brill][ Functional Morphology and Diversity] They have a large head, the hind edge of which covers the first thoracic segment. The thorax consists of nine limb-bearing segments (thoracic limb VIII absent in Lightiella), followed by 10 limbless abdominal segments and a
telson. 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.
[ Atlas of Crustacean Larvae] No eyes have been observed in either the adult or larval stages, presumably because of their muddy natural habitat. The second pair of antennae 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.
[ Rediscovery of the horseshoe shrimp Lightiella serendipita Jones, 1961 (Cephalocarida: Hutchinsoniellidae) in San Francisco Bay, California, USA, with a key to the worldwide species of Cephalocarida]
The mouth is located behind the large upper lip, flanked by mandibles. The first pair of maxillae 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.[
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Ecology
Cephalocaridans are found from the intertidal zone down to a depth of , in all kinds of . Cephalocaridans feed on marine detritus. To bring in food particles, they generate currents with the thoracic appendages like the and the . Food particles are then passed along a ventral groove, leading to the mouthparts.
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