The Cephalocarida, from

Ancient Greek Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...

κεφαλή (''kephalḗ''), meaning "head", and καρίς (''karís''), meaning "shrimp", are a

class Class, Classes, 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 d ...

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 Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

comprising only 12

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

. Both the nauplii and the adults are

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 the Ancient Greek word (), meaning "the depths". ...

. 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, closely related to hexapods, found in coastal aquifers which contain saline groundwater, with populations identified in almost every ocean basin so far explored, including in Australia, the Caribbean Se ...

in the Xenocarida. Although a second

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

, Lightiellidae, is sometimes used, all cephalocaridans are generally considered to belong in just one family: Hutchinsoniellidae.

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 preserve ...

records of cephalocaridans have been found in the

Ordovician The Ordovician ( ) is a geologic period and System (geology), system, the second of six periods of the Paleozoic Era (geology), Era, and the second of twelve periods of the Phanerozoic Eon (geology), Eon. The Ordovician spans 41.6 million years f ...

Castle Bank site.

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 A hermaphrodite () is a sexually reproducing organism that produces both male and female gametes. Animal species in which individuals are either male or female are gonochoric, which is the opposite of hermaphroditic. The individuals of many ...

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. They have a large head, the hind edge of which covers the first

thoracic The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of 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 ...

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 hindmost division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment (biology), segment of the arthropod body, or an additional division that is not a true segm ...

. 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 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 or foreshore is the area above water level at low tide and underwater at high tide; in other words, it is the part of the littoral zone within the tidal range. This area can include several types of habitats with various ...

down to a depth of , in all kinds of

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

s. Cephalocaridans feed on marine

detritus In biology, detritus ( or ) is organic matter made up of the decomposition, decomposing remains of organisms and plants, and also of feces. Detritus usually hosts communities of microorganisms that colonize and decomposition, decompose (Reminera ...

. To bring in food particles, they generate currents with the thoracic appendages like the

branchiopod Branchiopoda, from Ancient Greek βράγχια (''bránkhia''), meaning "gill", and πούς (''poús''), meaning "foot", is a class of crustaceans. It comprises fairy shrimp, clam shrimp, Diplostraca (or Cladocera), Notostraca, the Devonian ...

s and the

malacostraca Malacostraca is the second largest of the six classes of pancrustaceans behind insects, containing about 40,000 living species, divided among 16 orders. Its members, the malacostracans, display a great diversity of body forms and include crab ...

ns. Food particles are then passed

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

ly along a

ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. 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