Marine hatchetfish
Encyclopedia
Marine hatchetfishes or deep-sea hatchetfishes are small deep-sea mesopelagic
ray-finned fish of the stomiiform subfamily Sternoptychinae. They should not be confused with the freshwater hatchetfish
es, which are not particularly closely related Teleostei
in the characiform family Gasteropelecidae.
The scientific name means "Sternoptyx-subfamily", from Sternoptyx
(the type genus
) + the standard animal
family suffix
"-inae". It ultimately derives from Ancient Greek
stérnon (στέρνον, "breast") + ptýx (πτύξ, "a fold/crease") + Latin
forma ("external form"), the Greek part in reference to the thorax
shape of marine hatchetfishes.
, Pacific
and Indian Ocean
s, marine hatchetfishes range in size from Polyipnus danae at 2.8 cm (1.1 in) to the c.12 cm (4.7 in)-long Giant Hatchetfish
(Argyropelecus gigas). They are small deep-sea fishes which have evolved a peculiar body shape and like their relatives have bioluminescent photophore
s. The latter allow them to use counterillumination to escape predators that lurk in the depths: by matching the light intensity with the light penetrating the water from above, the fish does not appear darker if seen from below. They typically occur at a few hundred meters below the surface, but their entire depth range spans from 50 to 1,500 meters deep.
The body is deep and lateral
ly extremely compressed, somewhat resembling a hatchet
(with the thorax
being the "blade" and the caudal peduncle being the "handle"). The genus
Polyipnus
is rounded, the other two – in particular Sternoptyx
– decidedly angular if seen from the side. Their pelvis
is rotated to a vertical
position. The mouth is located at the tip of the snout and directed almost straight downwards.
Their scale
s are silvery, delicate and easily abraded. In some species, such as the Highlight Hatchetfish (Sternoptyx pseudobscura), large sections of the body at the base of the anal fin and/or caudal fin are transparent. They have perpendicular
spines and blade-like pterygiophores in front of the dorsal fin
. The anal fin has 11-19 rays and in some species
is divided in two parts; almost all have an adipose fin. Their large, sometimes tube-shaped eyes can collect the faintest of light and focus
well on objects both close and far. They are directed somewhat upwards, most conspicuously in the genus Argyropelecus
. This allows to discern the silhouette
s of prey moving overhead against the slightly brighter upper waters.
altogether:
Mesopelagic
The mesopelagic is that part of the pelagic zone that extends from a depth of 200 to 1000 metres below the ocean surface. It lies between the photic epipelagic above and the aphotic bathypelagic below, where there is no light at all...
ray-finned fish of the stomiiform subfamily Sternoptychinae. They should not be confused with the freshwater hatchetfish
Freshwater hatchetfish
The freshwater hatchetfishes are a family, Gasteropelecidae, of ray-finned fish. The common hatchetfish is the most popular member among fish keeping hobbyists...
es, which are not particularly closely related Teleostei
Teleostei
Teleostei is one of three infraclasses in class Actinopterygii, the ray-finned fishes. This diverse group, which arose in the Triassic period, includes 20,000 extant species in about 40 orders; most living fishes are members of this group...
in the characiform family Gasteropelecidae.
The scientific name means "Sternoptyx-subfamily", from Sternoptyx
Sternoptyx
Sternoptyx is an oceanic ray-finned fish genus which belongs in the family Sternoptychidae. This is the type genus of the Sternoptychidae, as well as the marine hatchetfish subfamily Sternoptychinae.It contains only four living species:...
(the type genus
Type genus
In biological classification, a type genus is a representative genus, as with regard to a biological family. The term and concept is used much more often and much more formally in zoology than it is in botany, and the definition is dependent on the nomenclatural Code that applies:* In zoological...
) + the standard animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
family suffix
Suffix
In linguistics, a suffix is an affix which is placed after the stem of a word. Common examples are case endings, which indicate the grammatical case of nouns or adjectives, and verb endings, which form the conjugation of verbs...
"-inae". It ultimately derives from Ancient Greek
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
stérnon (στέρνον, "breast") + ptýx (πτύξ, "a fold/crease") + Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
forma ("external form"), the Greek part in reference to the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
shape of marine hatchetfishes.
Description and ecology
Found in tropical and subtropical waters of the AtlanticAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, Pacific
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
and Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
s, marine hatchetfishes range in size from Polyipnus danae at 2.8 cm (1.1 in) to the c.12 cm (4.7 in)-long Giant Hatchetfish
Giant hatchetfish
The Giant Hatchetfish or Greater Silver Hatchetfish a marine hatchetfish of the genus Argyropelecus, is found in every ocean except the north Pacific in deep tropical and subtropical waters.-References:...
(Argyropelecus gigas). They are small deep-sea fishes which have evolved a peculiar body shape and like their relatives have bioluminescent photophore
Photophore
A photophore is a light-emitting organ which appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors...
s. The latter allow them to use counterillumination to escape predators that lurk in the depths: by matching the light intensity with the light penetrating the water from above, the fish does not appear darker if seen from below. They typically occur at a few hundred meters below the surface, but their entire depth range spans from 50 to 1,500 meters deep.
The body is deep and lateral
Anatomical terms of location
Standard anatomical terms of location are designations employed in science that deal with the anatomy of animals to avoid ambiguities that might otherwise arise. They are not language-specific, and thus require no translation...
ly extremely compressed, somewhat resembling a hatchet
Hatchet
A hatchet is a single-handed striking tool with a sharp blade used to cut and split wood...
(with the thorax
Thorax
The thorax is a division of an animal's body that lies between the head and the abdomen.-In tetrapods:...
being the "blade" and the caudal peduncle being the "handle"). The genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Polyipnus
Polyipnus
Polyipnus is an oceanic ray-finned fish genus which belongs in the family Sternoptychidae. This is the largest genus of the marine hatchetfishes and indeed of the entire Sternoptychidae...
is rounded, the other two – in particular Sternoptyx
Sternoptyx
Sternoptyx is an oceanic ray-finned fish genus which belongs in the family Sternoptychidae. This is the type genus of the Sternoptychidae, as well as the marine hatchetfish subfamily Sternoptychinae.It contains only four living species:...
– decidedly angular if seen from the side. Their pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
is rotated to a vertical
Vertical direction
In astronomy, geography, geometry and related sciences and contexts, a direction passing by a given point is said to be vertical if it is locally aligned with the gradient of the gravity field, i.e., with the direction of the gravitational force at that point...
position. The mouth is located at the tip of the snout and directed almost straight downwards.
Their scale
Scale (zoology)
In most biological nomenclature, a scale is a small rigid plate that grows out of an animal's skin to provide protection. In lepidopteran species, scales are plates on the surface of the insect wing, and provide coloration...
s are silvery, delicate and easily abraded. In some species, such as the Highlight Hatchetfish (Sternoptyx pseudobscura), large sections of the body at the base of the anal fin and/or caudal fin are transparent. They have perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...
spines and blade-like pterygiophores in front of the dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
. The anal fin has 11-19 rays and in some species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
is divided in two parts; almost all have an adipose fin. Their large, sometimes tube-shaped eyes can collect the faintest of light and focus
Focus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by...
well on objects both close and far. They are directed somewhat upwards, most conspicuously in the genus Argyropelecus
Argyropelecus
Argyropelecus is an oceanic ray-finned fish genus which belongs in the family Sternoptychidae. A collective name is "silver hatchetfishes", but this can also refer to a species of the freshwater hatchetfishes which are not particularly closely related but merely convergent...
. This allows to discern the silhouette
Silhouette
A silhouette is the image of a person, an object or scene consisting of the outline and a basically featureless interior, with the silhouetted object usually being black. Although the art form has been popular since the mid-18th century, the term “silhouette” was seldom used until the early decades...
s of prey moving overhead against the slightly brighter upper waters.
Genera
There are three genera in this subfamily, with some 40 speciesSpecies
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
altogether:
- ArgyropelecusArgyropelecusArgyropelecus is an oceanic ray-finned fish genus which belongs in the family Sternoptychidae. A collective name is "silver hatchetfishes", but this can also refer to a species of the freshwater hatchetfishes which are not particularly closely related but merely convergent...
– silver hatchetfishes (7 species) - PolyipnusPolyipnusPolyipnus is an oceanic ray-finned fish genus which belongs in the family Sternoptychidae. This is the largest genus of the marine hatchetfishes and indeed of the entire Sternoptychidae...
(32 species) - SternoptyxSternoptyxSternoptyx is an oceanic ray-finned fish genus which belongs in the family Sternoptychidae. This is the type genus of the Sternoptychidae, as well as the marine hatchetfish subfamily Sternoptychinae.It contains only four living species:...
(4 species)