The Cephalocarida are a
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
in the
subphylum Crustacea
Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
comprising only 12
benthic
The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from ancient Greek, βένθος (bénthos), meaning "t ...
species. They were discovered in 1955 by
Howard L. Sanders
Howard is an English-language given name originating from Old French Huard (or Houard) from a Germanic source similar to Old High German ''*Hugihard'' "heart-brave", or ''*Hoh-ward'', literally "high defender; chief guardian". It is also probab ...
, and are commonly referred to as horseshoe shrimp. They have been grouped together with the
Remipedia in the
Xenocarida. Although a second
family, Lightiellidae, is sometimes used, all cephalocaridans are generally considered to belong in just one family: Hutchinsoniellidae. Though no
fossil record of cephalocaridans has been found, most specialists believe them to be primitive among crustaceans.
Taxonomy
* Class Cephalocarida
Sanders 1955
** Order Brachypoda
Birshteyn 1960
*** Family Hutchinsoniellidae
Sanders 1955
**** Genus ''
Chiltoniella''
Knox & Fenwick 1977
***** ''Chiltoniella elongata''
Knox & Fenwick 1977
**** Genus ''
Hampsonellus''
Hessler & Wakabara 2000
***** ''Hampsonellus brasiliensis''
Hessler & Wakabara 2000
**** Genus ''
Hutchinsoniella
''Hutchinsoniella macracantha'' is a species of crustacean known as a horseshoe shrimp. It is the only species in the genus ''Hutchinsoniella'' and was first described in 1955 by Howard L. Sanders, having been discovered in Long Island Sound; th ...
''
Sanders 1955
***** ''Hutchinsoniella macracantha''
Sanders 1955
**** Genus ''
Lightiella''
Jones 1961
***** ''Lightiella floridana''
McLaughlin 1976
***** ''Lightiella incisa''
Gooding 1963
***** ''Lightiella magdalenina''
Carcupino et al. 2006
***** ''Lightiella monniotae''
Cals & Delamare Deboutteville 1970
***** ''Lightiella serendipita''
Jones 1961
**** Genus ''
Sandersiella''
Shiino 1965
***** ''Sandersiella acuminata''
Shiino 1965
***** ''Sandersiella bathyalis''
Hessler & Sanders 1973
***** ''Sandersiella calmani''
Hessler & Sanders 1973
***** ''Sandersiella kikuchii''
Shimomura & Akiyama 2008
Description and anatomy
These are
hermaphroditic crustaceans with an elongated body that measures in length. 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. 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.
The mouth is located behind the large upper lip, flanked by
mandibles. The first pair of
maxillae
The maxilla (plural: ''maxillae'' ) in vertebrates is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The t ...
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.
[
]
Ecology
Cephalocaridans are found from the intertidal zone
The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
down to a depth of , in all kinds of sediments. Cephalocaridans feed on marine detritus
In biology, detritus () is dead particulate organic material, as distinguished from dissolved organic material. Detritus typically includes the bodies or fragments of bodies of dead organisms, and fecal material. Detritus typically hosts commun ...
. To bring in food particles, they generate currents with the thoracic appendages like the branchiopods and the malacostracans. Food particles are then passed anterior
Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
ly along a ventral groove, leading to the mouthparts
Mouthparts may refer to:
* The parts of a mouth
** Arthropod mouthparts
*** Insect mouthparts
{{disambig ...
.
References
External links
Cephalocarida- University of California Museum of Paleontology
*
{{Taxonbar, from=Q132649
Crustacean taxonomy
Arthropod classes