''Idiastion'' is a small

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of marine

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

belonging to the

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 ...

Scorpaenidae The Scorpaenidae (also known as scorpionfish) are a family (biology), family of mostly ocean, marine fish that includes many of the world's most venomous species. As their name suggests, scorpionfish have a type of "sting" in the form of sharp ...

, the scorpionfishes. They are found in the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

and

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

oceans.

Taxonomy

''Idiastion'' was first described as a genus by the American

ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 35,800 species of fish had been described as of March 2 ...

William N. Eschmeyer in 1965 when he was describing its

type species In International_Code_of_Zoological_Nomenclature, 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 spe ...

, ''Idiastion kyphos'', from the southeastern

Caribbean Sea The Caribbean Sea is a sea of the Atlantic Ocean, North Atlantic Ocean in the tropics of the Western Hemisphere, located south of the Gulf of Mexico and southwest of the Sargasso Sea. It is bounded by the Greater Antilles to the north from Cuba ...

, between Venezuela and Grenada. Subsequently two more species have been added to the genus from the Pacific Ocean. The genus is classified within the

tribe The term tribe is used in many different contexts to refer to a category of human social group. The predominant worldwide use of the term in English is in the discipline of anthropology. The definition is contested, in part due to conflict ...

Scorpaenini 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 botanical subfamily names with "-oideae", and zo ...

Scorpaeninae Scorpaeninae is a subfamily of ray-finned fish belonging to the family Scorpaenidae in the order Scorpaeniformes, it includes the scorpionfishes, the lionfishes and turkeyfishes. They bear venomous spines in the anal, dorsal and pelvic fins which ...

of the scorpionfish family Scorpaenidae. The genus name ''Idiastion'' is the

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

word meaning "hermit" or "recluse", alluding to the rarity of the scorpionfishes at the depths at which ''Idiastion'' was collected from.

Species

There are currently three recognized

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), ...

in this genus: * ''Idiastion hageyi'' McCosker, 2008(Galapagos humpback scorpionfish) * ''Idiastion kyphos'' Eschmeyer, 1965 (Sharpcheek scorpionfish) * ''Idiastion pacificum'' Ishida & Amaoka, 1992 (Flame humpback scorpionfish)

Characteristics

''Idiastion'' scorpionfishes have a deep body, deepest behind the head with a hump backed shape. They have well-developed, robust spines which can have more than one point. They do not have an occipital pit behind their large eyes which have a suborbital ridge armed with between 5 and 8 spines. There are 4 spines on the preoperculum with the uppermost one being the longest and being located some distance from the other 3 spines. They have small, simple teeth on the jaws and the roof of the mouth. They have 12 spines and 9 soft rays in the

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

and 3 spines and 5 soft rays in the

anal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

. The

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

has 17–19 rays, the central rays being the longest and the uppermist ray and bottom 7–9 rays are unbranched with the lower ones being fleshy with their tips protruding beyond the membrane. They have a complete

lateral line The lateral line, also called the lateral line organ (LLO), is a system of sensory organs found in fish, used to detect movement, vibration, and pressure gradients in the surrounding water. The sensory ability is achieved via modified epithelia ...

with tubes on the scales and a small

swim bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled organ (anatomy), organ in bony fish that functions to modulate buoyancy, and thus allowing the fish to stay at desired water depth without having to maintain lift ...

. These scorpionfishes are small fishes with standard lengths ranging from in ''I. kyphos'' and in ''I. pacificum''.

Distribution and habitat

''Idiastion'' scorpionfishes are found in the western Atlantic Ocean (''I. kyphos''), the

Galápagos Islands The Galápagos Islands () are an archipelago of volcanic islands in the Eastern Pacific, located around the equator, west of the mainland of South America. They form the Galápagos Province of the Republic of Ecuador, with a population of sli ...

(''I. hageyi'') and around Japan and over the Emperor Seamounts in the northwestern Pacific (''I. pacificum''). They live close to the bottom over reefs and soft substrates.

References

{{Taxonbar, from=Q1882947 Scorpaenini Marine fish genera Taxa named by William N. Eschmeyer