''Cryothenia'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

of marine

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species. The ray-finned fishes are so called because their fins are webs of skin supported by bony or hor ...

es, belonging to the

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

Nototheniidae : ''In some scientific literature, the term "cod icefish" is used to identify members of this family. This should not be confused with the term "icefish," which refers to the "white-blooded" fishes of the family Channichthyidae. See Icefish (disam ...

, the notothens or cod icefishes. They are native to the

Southern Ocean The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...

Taxonomy

''Cryothenia'' was first formally described as a genus in 1981 by Robert A. Daniels when he was describing the new species ''Cryothenia peninsulae'', which he designated as the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

as well as being the only species in the genus then known. Some authorities place this genus in the

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

Trematominae, but the 5th edition of ''

Fishes of the World ''Fishes of the World'' by the American ichthyologist Joseph S. Nelson (1937–2011) is a standard reference for fish systematics. Now in its fifth edition (2016), the work is a comprehensive overview of the diversity and classification of the ...

'' does not include subfamilies in the Nototheniidae. The genus name is a compound of ''cryo'', meaning "ice", and ''thenia'', which means "coming from", that is an "icefish".

Species

The recognized species in this genus are: * ''

Cryothenia amphitreta ''Cryothenia amphitreta'' is a species of marine ray-finned fish, belonging to the family Nototheniidae, the notothens or cod icefishes. It is found in the Antarctic Ross Sea. Taxonomy ''Cryothenia amphitreta'' was first formally described in ...

'' Cziko & C. H. C. Cheng, 2006 * ''

Cryothenia peninsulae ''Cryothenia'' is a genus of marine ray-finned fishes, belonging to the family Nototheniidae, the notothens or cod icefishes. They are native to the Southern Ocean. Taxonomy ''Cryothenia'' was first formally described as a genus in 1981 by Rober ...

'' Daniels, 1981 (pithead)

Characteristics

''Cryothenia'' fishes have an elongate, fusiform body with a flattened head and a large mouth which has the lower jaw protruding and the maxilla extending beyond the front of the eye. The sensory canal on the head have large and obvious pores. There are no tubular scales in either of the two lateral lines, the upper lateral line consists of pored scales and follows the dorsal profile of the body from gill opening to underneath the rear part of the second

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

. A middle lateral line also comprises pored scales and runs along the middle of the flanks from the pectoral fin to base of the caudal fin. Front part of the head does not have scales. They do not have any elongated fin spines or rays. The rounded caudal fin rounded contains 12 branched rays. The maximum recorded total length on this genus was the holotype of ''C. amphitreta'' which had a

standard length Fish measurement is the measuring of individual fish and various parts of their anatomies. These data are used in many areas of ichthyology, including taxonomy and fisheries biology. Overall length * Standard length (SL) is the length of a fish m ...

of .

Distribution, habitat and biology

''Cryothenia'' are found in the Southern Ocean, with ''C. peninsulae'' being found along the west coast

Antarctic Peninsula The Antarctic Peninsula, known as O'Higgins Land in Chile and Tierra de San Martín in Argentina, and originally as Graham Land in the United Kingdom and the Palmer Peninsula in the United States, is the northernmost part of mainland Antarctic ...

and ''C. amphitreta'' only being recorded in the

McMurdo Sound McMurdo Sound is a sound in Antarctica. It is the southernmost navigable body of water in the world, and is about from the South Pole. Captain James Clark Ross discovered the sound in February 1841, and named it after Lt. Archibald McMurdo o ...

, ''C. peninsulae'' feed on

krill Krill are small crustaceans of the order Euphausiacea, and are found in all the world's oceans. The name "krill" comes from the Norwegian Norwegian, Norwayan, or Norsk may refer to: *Something of, from, or related to Norway, a country in n ...

and these fishes are regarded as pelagic or epibenthic. ''C. amphitreta'' was found to have blood which contained a high level of

antifreeze protein Antifreeze proteins (AFPs) or ice structuring proteins refer to a class of polypeptides produced by certain animals, plants, fungi and bacteria that permit their survival in temperatures below the freezing point of water. AFPs bind to small i ...

s, but this has not been tested for ''C. peninsulae''.

References

{{Taxonbar, from=Q1157140 Nototheniidae