The longfin escolar, ''Scombrolabrax heterolepis'', also known as the black mackerel, is a widespread but uncommon deep sea

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 ...

that presents some difficulties for

taxonomy image:Hierarchical clustering diagram.png, 280px, Generalized scheme of taxonomy Taxonomy is a practice and science concerned with classification or categorization. Typically, there are two parts to it: the development of an underlying scheme o ...

. It is placed in its own family Scombrolabracidae, but the family's placement in 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 ...

s of

Perciformes Perciformes (), also called the Acanthopteri, is an order or superorder of ray-finned fish in the clade Percomorpha. ''Perciformes'' means " perch-like". Among the well-known members of this group are perches and darters ( Percidae), and als ...

has included

Scombroidei Scombroidei or Scombrales is a suborder or infraorder of the order Scombriformes or suborder Scombroidei. The suborder or infraorder includes the tunas, mackerel and snake-mackerels. Regular scombrids are observed to have large heads, eyes, and ...

Percoidei Percoidei is a suborder of bony fishes in the order Perciformes. Many commercially harvested fish species are considered to be contained in this suborder, including the groupers, Serranidae, seabasses and perches. Divisions The following classif ...

, and Trichiuroidei, while some authors place it in its own suborder Scombrolabracoidei and even in its own order the Scombrolabraciformes. The fish bears some resemblance to members of

Gempylidae The Gempylidae are a family of scombriform ray-finned fishes commonly known as snake mackerels or escolars. The family includes about 25 species. They are elongated fishes with a similar appearance to barracudas, having a long dorsal fin, usuall ...

, but has protrusible

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 ...

e, serrated opercles and

preopercle The operculum is a series of bones found in bony fish and chimaeras that serves as a facial support structure and a protective covering for the gills; it is also used for respiration and feeding. Anatomy The opercular series contains four bon ...

s, and a spur on the lowest principal caudal ray, all of which are characteristic of percoids. Its color varies from black to dark brown. This fish is known to grow to 30 cm in length. The body is covered in soft scales which easily slough off when handled. The eyes are large with usually a single pair of elongated teeth in the middle of the top jaw. The longfin escolar is unique among fishes for having several of its

vertebra Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

e hollowed out and filled by

evagination Endodermic evagination relates to the inner germ layers of cells of the very early embryo, from which is formed the lining of the digestive tract, of other internal organs, and of certain glands, implies the extension of a layer of body tissue to f ...

s of the

gas bladder The swim bladder, gas bladder, fish maw, or air bladder is an internal gas-filled 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 via swimming, ...

. It is most often encountered as a bycatch species in pelagic longline fisheries.

References

* * * * J. S. Nelson, ''

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 ...

''. Scombriformes Fish described in 1921 {{Scombroidei-stub