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 In zoological nomenclature, a subphylum is a taxonomic rank below the rank of phylum. The taxonomic rank of " subdivision" in fungi and plant taxonomy is equivalent to "subphylum" in zoological taxonomy. Some plant taxonomists have also used th ...

Crustacea comprising only 12 benthic

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. They were discovered in 1955 by Howard L. Sanders, and are commonly referred to as horseshoe shrimp. They have been grouped together with the

Remipedia Remipedia is a class of blind crustaceans found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Sea, and the Atlantic Ocean. The ...

in the

Xenocarida Xenocarida (from the Greek language, Greek for ''strange shrimp'') is a proposed clade inside the subphylum Crustacean, Crustacea that comprises two classes that were discovered in the 20th century: Remipedia and Cephalocarida. The clade was recov ...

. Although a second

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

, Lightiellidae, is sometimes used, all cephalocaridans are generally considered to belong in just one family: Hutchinsoniellidae. Though no

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

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'' 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 In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have s ...

crustaceans with an elongated body that measures in length. They have a large head, the hind edge of which covers the first

thoracic The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the crea ...

segment. The thorax consists of nine limb-bearing segments (thoracic limb VIII absent in Lightiella), followed by 10 limbless abdominal segments and a

telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...

. 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 In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

. 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.

Ecology

Cephalocaridans are found from the intertidal zone down to a depth of , in all kinds of

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

s. Cephalocaridans feed on marine detritus. To bring in food particles, they generate currents with the thoracic appendages like the

branchiopod Branchiopoda is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Diplostraca (or Cladocera), Notostraca and the Devonian '' Lepidocaris''. They are mostly small, freshwater animals that feed on plankton and detritus. Descript ...

s and the

malacostraca Malacostraca (from New Latin; ) is the largest of the six classes of crustaceans, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crabs, l ...

ns. Food particles are then passed anteriorly along a

ventral 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 ...

groove, leading to the mouthparts.

References

External links

Cephalocarida- University of California Museum of Paleontology
* {{Taxonbar, from=Q132649 Crustacean taxonomy Arthropod classes