''Acentrophryne'' is a

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 ...

deep-sea The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of or the point of transition from continental shelves to continental slopes. Conditions within the deep sea are a combination of low tempe ...

anglerfish The anglerfish are ray-finned fish in the order Lophiiformes (). Both the order's common name, common and scientific name comes from the characteristic mode of predation, in which a modified dorsal Fish fin#Ray-fins, fin ray acts as a Aggressiv ...

in 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 ...

Linophrynidae, the leftvents, known from the eastern

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, 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 ...

. Fossils of the type species, ''A. longidens'', have been found in Late

Miocene The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...

-aged

Puente Formation The Puente Formation is a Formation (geology), geologic formation in California. It preserves fossils dating back to the middle to upper Miocene epoch of the Neogene Period (geology), period, most of which were deposited in a deepwater environment ...

Rosedale, California Rosedale is a census-designated place (CDP) in Kern County, California, United States. The population was 14,058 at the 2010 census, up from 8,445 at the 2000 census. Formerly a country town west of Bakersfield, it is now surrounded by suburban ...

Taxonomy

''Acentrophryne'' was first proposed as a

monospecific genus In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

in 1926 by the English

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 ...

Charles Tate Regan Charles Tate Regan (1 February 1878 – 12 January 1943) was a British ichthyology, ichthyologist, working mainly around the beginning of the 20th century. He did extensive work on fish classification schemes. Born in Sherborne, Dorset, he was ...

when he described ''Acentrophryne longidens'' as a new species. ''A. longidens'' was described by Regan from a

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

collected at 7°30'N, 79°19'W in the

Gulf of Panama The Gulf of Panama () is a gulf of the Pacific Ocean off the southern coast of Panama, where most of eastern Panama's southern shores adjoin it. The Gulf has a maximum width of , a maximum depth of and the size of . The Panama Canal connects the ...

from a depth of around by the Danish research vessel '' Dana''. The 5th edition of ''

Fishes of the World ''Fishes of the World'' is a standard reference for the systematics of fishes. It was first written in 1976 by the American ichthyologist Joseph S. Nelson (1937–2011). Now in its fifth edition (2016), the work is a comprehensive overview of t ...

'' classifies this genus within the family Linophrynidae, which it places within the

suborder Order () is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and recognized ...

Ceratioidei Ceratioidei, the deep-sea anglerfishes or pelagic anglerfishes, is a suborder of marine ray-finned fishes, one of five suborders in the order Lophiiformes, the anglerfishes. These fishes are found in tropical and temperate seas throughout the wor ...

, the deep sea anglerfishes, within the order Lophiiformes, the anglerfishes.

Etymology

''Acentrophryne'' prefixes ''a'', meaning "without", to ''kentron'', meaning "spine", a reference to the lack of a spine on the

preoperculum This glossary of ichthyology is a list of definitions of terms and concepts used in ichthyology, the study of fishes. A B C ...

. This is then suffixed with ''phryne'', which means "toad", commonly used in the names of anglerfish genera. Its use may date as far back as

Aristotle Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...

and

Cicero Marcus Tullius Cicero ( ; ; 3 January 106 BC – 7 December 43 BC) was a Roman statesman, lawyer, scholar, philosopher, orator, writer and Academic skeptic, who tried to uphold optimate principles during the political crises tha ...

, who referred to anglerfishes as "fishing-frogs" and "sea-frogs", respectively, possibly because of their resemblance to frogs and toads.

Species

''Acentrophryne'' contains the following recognized valid species: * ''

Acentrophryne dolichonema ''Acentrophryne dolichonema'' is a species of marine ray-finned fish belonging to the family Linophrynidae, the leftvents, a family of deep sea anglerfishes. This species is only known from the eastern Pacific Ocean off the coast of Peru. Tax ...

'' Pietsch & Shimazaki, 2005 * ''

Acentrophryne longidens ''Acentrophryne longidens'' is a species of Marine life, marine Actinopterygii, ray-finned fish belonging to the Family (biology), family leftvent, Linophryidae, the leftvents, a family of Ceratioidei, deep sea anglerfishes. This species is only k ...

'' Regan, 1926

Characteristics

''Acentrophryne'' is known only from

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

females; the males and larvae are unknown. These females differ from the other genera of leftvents by the absence of a spine on the preoperculum. They also have no spines on the frontal, epiotic, and posttemporal bones and a smaller number of teeth, 6 to 26

premaxilla The premaxilla (or praemaxilla) is one of a pair of small cranial bones at the very tip of the upper jaw of many animals, usually, but not always, bearing teeth. In humans, they are fused with the maxilla. The "premaxilla" of therian mammals h ...

ry teeth and 9 to 16 on each side of the lower jaw. These teeth are very long and are arranged in two or three series of oblique rows, which overlap. There are also between 2 and 6 teeth on the

vomer The vomer (; ) is one of the unpaired facial bones of the skull. It is located in the midsagittal line, and articulates with the sphenoid, the ethmoid, the left and right palatine bones, and the left and right maxillary bones. The vomer forms ...

. The ninth ray of the

caudal 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 only ...

is around half the length of the eighth. The

illicium ''Illicium'' is a genus of flowering plants treated as part of the family Schisandraceae,

has a length that is equivalent to between 35.7% and 70.5% of the

standard length Fish measurement is the measuring of individual fish and various parts of fish anatomy, their anatomies, for data used in many areas of ichthyology, including Taxonomy (biology), taxonomy and fishery biology. Overall length Standard length (SL) is ...

, and the esca has one distal appendage, which lacks pigment. There is no hyoid barbel. Apart from the distal appendage, these fishes are uniformly black. The largest species in the genus is ''A. dolichonema'' with a maximum published standard length of .

Distribution and habitat

''Acentrophryne'' leftvents are known only from the eastern Pacific Ocean, where they have been recorded off Costa Rica, Panama, Colombia and Peru at depths between .

Fossil record

''Acentophryne'' is known from the fossil record as a single specimen was found in 1977 from a

diatomaceous deposit in the

Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...

. This was initially tentatively identified as being ''A. longidens'' but its identity is now left open as ''Acentrophryne sp.''. ''Acentrophryne'' leftvents are endemic to the eastern Pacific and are adapted to low oxygen environments. The fossil specimen from California suggests that this genus originated in the Miocene and that hypoxic environments were more widespread in the eastern Pacific, as these reduced the genus underwent a contraction in its distribution and subsequent

allopatric speciation Allopatric speciation () – also referred to as geographic speciation, vicariant speciation, or its earlier name the dumbbell model – is a mode of speciation that occurs when biological populations become geographically isolated from ...

References

{{Taxonbar, from=Q1811463 Linophrynidae Marine fish genera Taxa named by Charles Tate Regan