Stomiiformes
Encyclopedia
Stomiiformes is an order
of deep-sea ray-finned fishes of very diverse morphology
. It includes for example dragonfish
es, lightfish
es, loosejaws, marine hatchetfish
es and viperfish
es. The order contains 4 families
(5 according to some authors) with more than 50 genera
and almost 400 species
. As usual for deep-sea fishes, there are few common names for species of the order, but the Stomiiformes as a whole are often called dragonfishes and allies or simply stomiiforms.
The scientific name means "Stomias-shaped", from Stomias (the type genus
) + the standard fish
order suffix
"-formes". It ultimately derives from Ancient Greek
stóma (στόμᾶ, "mouth") + Latin
forma ("external form"), the former in reference to the huge mouth opening of these fishes.
waters up to subarctic
or even Antarctic
ones.
The smallest species of this order is the bristlemouth Cyclothone pygmaeae. Native to the Mediterranean Sea
, it reaches just 1.5 cm (0.6 in) as an adult. The largest species is the barbeled dragonfish Opostomias micripnis, widely found in the Atlantic
, Indian
and Pacific Ocean
s and measuring about 50 cm (19.7 in) in adult length.
These fish have a highly unusual and often almost nightmarish appearance. They all have teeth on the premaxilla
and maxilla
. Their maxillary ligament
s, as well as some muscles and certain bones in the branchial cavity, are specialized in a distinctive way. Most have large mouths extending back past the eyes. Some also have a chin barbel
. The dorsal
and/or pectoral fins are missing in some, but others have a adipose fin. The pelvic fin has 4-9 rays, and the stomiiforms possess 5-24 branchiostegal rays. Their scale
s are cycloid, delicate and easily sloughed off; some are scaleless. The coloration is typically dark brown or black; a few (mostly Gonostomatoidei) are silver, and photophore
s (light-producing organs) are common in this order.
As common for deep-sea creatures, all members of Stomiiformes (except one) have photophore
s, whose structure is characteristic of the order. The light emitted can be more or less strong and its color can be light yellow, white, violet or red. The light coming from these fish is generally invisible to their prey. The lighting mechanism can be very simple – consisting of small gleaming points on the fish body – or very elaborate, involving lens
es and refractors.
The most common arrangement is one or two rows of photophores on the ventral aspect of the body. The rows run from the head down to the tip of the tail. Photophores are also present in chin barbels of the family Stomiidae
. The light produced in these glandular organs is the product of an enzymatic reaction, a catylization of coelenterazine
by calcium ions.
ic invertebrate
s. During the night, these Stomiiformes hunt and feed on such organisms, swimming back to deeper waters when the sun rises. They apparently are able to measure the intensity of the sunlight that reaches them. They will thus move to stay always in the zone where light intensity
is very low, though it is not entirely dark.
This daily migration is well observed at quite a few species of stomiiforms. However, it is also performed by other fishes, while some larger Stomiiformes – among them the largest predators of the deep sea – stay in their habitat
all the time and feed on smaller migrating fish that return from the surface.
generally in deep seas, but the eggs are light and float towards the ocean surface. They hatch in surface waters. When the larva
e have completed their metamorphosis and look like adults, they descend to join the main population.
Like a lot of benthic fish species, certain members of the order – especially in the genera Cyclothone and Gonostoma – change their sex during their life. When they become sexually mature, they are males; later on they transform into females.
, usually together with the Ateleopodiformes (jellynoses), but sometimes on their own. Whether it is indeed justified to accept such a small group is doubtful; it may well be that the closest living relatives of the "Stenopterygii" are found among the superorder Protacanthopterygii
, and that the former would need to be merged in the latter. In some classifications, the "Stenopterygii" are kept separate but included with the Protacanthopterygii and the monotypic
superorder Cyclosquamata in an unranked clade
called Euteleostei. That would probably require splitting two additional monotypic superorders out of the Protacanthopterygii, and thus result in a profusion of very small taxa.
The Stomiiformes have also been considered close relatives of the Aulopiformes
. The latter are otherwise placed in a monotypic superorder "Cyclosquamata" but also appear to be quite close to the Protacanthopterygii indeed. The relationships of these – and the Lampriformes
or Myctophiformes
, which are also usually treated as monotypic superorders – to the taxa mentioned before is still not well resolved at all, and regardless whether one calls them Protacanthopterygii sensu lato or Euteleostei, the phylogeny of this group of moderately-advanced Teleostei is in need of further study.
The ancestral Stomiiformes probably had thin brownish bodies, rows of egg-shaped photophore
s adorning the lower body parts, and mouths with numerous teeth. From these, two lineages evolved, probably some time during the Late Cretaceous
: Among the modern Stomiiformes, the Gonostomatidae
and Phosichthyidae
are phenetically very similar, but this is due to their being very plesiomorphic and retaining many traits of the original stomiiforms. Each of the two has characteristic synapomorphies with one of the more advanced stomiiform families – the Sternoptychidae
and the Stomiidae
, respectively. These two, in turn, are highly autapomorphic, and at a casual glance do not look as if they were as closely related to the other stomiiforms as they actually are.
Thus, the classification of the suborders and families
of the Stomiiformes is:
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of deep-sea ray-finned fishes of very diverse morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
. It includes for example dragonfish
Dragonfish
-Other fish called Dragonfish:*Barbeled dragonfish, small bioluminescent deep-sea stomiiform fish of the family Stomiidae*Arowana, large freshwater osteoglossiform fish of the family Osteoglossidae...
es, lightfish
Lightfish
Lightfish refers to two groups of bioluminescent fishes:* Family Phosichthyidae.* Bristlemouths in the family Gonostomatidae....
es, loosejaws, marine hatchetfish
Marine hatchetfish
Marine hatchetfishes or deep-sea hatchetfishes are small deep-sea mesopelagic ray-finned fish of the stomiiform subfamily Sternoptychinae...
es and viperfish
Viperfish
A viperfish is a saltwater fish in the genus Chauliodus, with long, needle-like teeth and hinged lower jaws. They grow to lengths of 30 to 60 cm . Viperfish stay near lower depths in the daytime and shallow at night. Viperfish mainly stay in tropical and temperate waters...
es. The order contains 4 families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
(5 according to some authors) with more than 50 genera
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...
and almost 400 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...
. As usual for deep-sea fishes, there are few common names for species of the order, but the Stomiiformes as a whole are often called dragonfishes and allies or simply stomiiforms.
The scientific name means "Stomias-shaped", from Stomias (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 fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
order 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...
"-formes". 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...
stóma (στόμᾶ, "mouth") + 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 former in reference to the huge mouth opening of these fishes.
Description and ecology
Members of this order are mostly pelagic fishes living in deep oceanic waters. Their distribution around the world's oceans is very wide, ranging from subtropical and temperateTemperate
In geography, temperate or tepid latitudes of the globe lie between the tropics and the polar circles. The changes in these regions between summer and winter are generally relatively moderate, rather than extreme hot or cold...
waters up to subarctic
Subarctic
The Subarctic is a region in the Northern Hemisphere immediately south of the true Arctic and covering much of Alaska, Canada, the north of Scandinavia, Siberia, and northern Mongolia...
or even Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
ones.
The smallest species of this order is the bristlemouth Cyclothone pygmaeae. Native to the Mediterranean Sea
Mediterranean Sea
The Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, it reaches just 1.5 cm (0.6 in) as an adult. The largest species is the barbeled dragonfish Opostomias micripnis, widely found in the Atlantic
Atlantic 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...
, Indian
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...
and Pacific Ocean
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...
s and measuring about 50 cm (19.7 in) in adult length.
These fish have a highly unusual and often almost nightmarish appearance. They all have teeth on the premaxilla
Premaxilla
The incisive bone is the portion of the maxilla adjacent to the incisors. It is a pair of small cranial bones at the very tip of the jaws of many animals, usually bearing teeth, but not always. They are connected to the maxilla and the nasals....
and maxilla
Maxilla
The maxilla is a fusion of two bones along the palatal fissure that form the upper jaw. This is similar to the mandible , which is also a fusion of two halves at the mental symphysis. Sometimes The maxilla (plural: maxillae) is a fusion of two bones along the palatal fissure that form the upper...
. Their maxillary ligament
Ligament
In anatomy, the term ligament is used to denote any of three types of structures. Most commonly, it refers to fibrous tissue that connects bones to other bones and is also known as articular ligament, articular larua, fibrous ligament, or true ligament.Ligament can also refer to:* Peritoneal...
s, as well as some muscles and certain bones in the branchial cavity, are specialized in a distinctive way. Most have large mouths extending back past the eyes. Some also have a chin barbel
Barbel (anatomy)
A barbel on a fish is a slender, whiskerlike tactile organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, sturgeon, the zebrafish and some species of shark...
. The dorsal
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...
and/or pectoral fins are missing in some, but others have a adipose fin. The pelvic fin has 4-9 rays, and the stomiiforms possess 5-24 branchiostegal rays. 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 cycloid, delicate and easily sloughed off; some are scaleless. The coloration is typically dark brown or black; a few (mostly Gonostomatoidei) are silver, and 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 (light-producing organs) are common in this order.
Bioluminescence
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, whose structure is characteristic of the order. The light emitted can be more or less strong and its color can be light yellow, white, violet or red. The light coming from these fish is generally invisible to their prey. The lighting mechanism can be very simple – consisting of small gleaming points on the fish body – or very elaborate, involving lens
Lens (optics)
A lens is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam. A simple lens consists of a single optical element...
es and refractors.
The most common arrangement is one or two rows of photophores on the ventral aspect of the body. The rows run from the head down to the tip of the tail. Photophores are also present in chin barbels of the family Stomiidae
Stomiidae
Stomiidae is a family of deep-sea ray-finned fish, including the barbeled dragonfishes, stareaters and loosejaws.Stomiids are generally elongated fish with black or near-black bodies, but they are highly variable in form, and are sometimes grouped into multiple different families as a result. The...
. The light produced in these glandular organs is the product of an enzymatic reaction, a catylization of coelenterazine
Coelenterazine
Coelenterazine is the luciferin, the light-emitting molecule, found in many aquatic organisms across seven phyla. It is the substrate in many luciferases and photoproteins including Renilla reniformis luciferase , Gaussia luciferase , aequorin, and obelin.-History:Coelenterazine was simultaneously...
by calcium ions.
Daily migration
During the day, Stomiiformes stay in deep waters. When the sun sets, most of them follow the dimming sunlight up to near-surface waters, which are richer in animal life such as small fishes and planktonPlankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
ic invertebrate
Invertebrate
An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...
s. During the night, these Stomiiformes hunt and feed on such organisms, swimming back to deeper waters when the sun rises. They apparently are able to measure the intensity of the sunlight that reaches them. They will thus move to stay always in the zone where light intensity
Light intensity
Several measures of light are commonly known as intensity. These are obtained by dividing either a power or a luminous flux by a solid angle, a planar area, or a combination of the two...
is very low, though it is not entirely dark.
This daily migration is well observed at quite a few species of stomiiforms. However, it is also performed by other fishes, while some larger Stomiiformes – among them the largest predators of the deep sea – stay in their habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
all the time and feed on smaller migrating fish that return from the surface.
Reproduction
Stomiiforms spawnSpawn (biology)
Spawn refers to the eggs and sperm released or deposited, usually into water, by aquatic animals. As a verb, spawn refers to the process of releasing the eggs and sperm, also called spawning...
generally in deep seas, but the eggs are light and float towards the ocean surface. They hatch in surface waters. When the larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e have completed their metamorphosis and look like adults, they descend to join the main population.
Like a lot of benthic fish species, certain members of the order – especially in the genera Cyclothone and Gonostoma – change their sex during their life. When they become sexually mature, they are males; later on they transform into females.
Systematics
The Stomiiformes are often placed in the teleost superorder StenopterygiiStenopterygii
Stenopterygii are a superorder of ray-finned fish in the infraclass Teleostei. Their validity is somewhat doubtful, as the group was established to separate, out of a large group of closely related Teleostei, a mere two rather peculiarly autapomorphic orders at best...
, usually together with the Ateleopodiformes (jellynoses), but sometimes on their own. Whether it is indeed justified to accept such a small group is doubtful; it may well be that the closest living relatives of the "Stenopterygii" are found among the superorder Protacanthopterygii
Protacanthopterygii
Protacanthopterygii is a ray-finned fish taxon ranked as a superorder of the infraclass Teleostei. They inhabit both marine and freshwater habitat...
, and that the former would need to be merged in the latter. In some classifications, the "Stenopterygii" are kept separate but included with the Protacanthopterygii and the monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
superorder Cyclosquamata in an unranked clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
called Euteleostei. That would probably require splitting two additional monotypic superorders out of the Protacanthopterygii, and thus result in a profusion of very small taxa.
The Stomiiformes have also been considered close relatives of the Aulopiformes
Aulopiformes
Aulopiformes is an order of marine ray-finned fish consisting of some 15 extant and several prehistoric families with about 45 genera and over 230 species. The common names grinners, lizardfishes and allies or aulopiforms are sometimes used for this group...
. The latter are otherwise placed in a monotypic superorder "Cyclosquamata" but also appear to be quite close to the Protacanthopterygii indeed. The relationships of these – and the Lampriformes
Lampriformes
Lampriformes is an order of ray-finned fish. They are collectively called "lamprids" or lampriforms, and unite such open-ocean and partially deep-sea Teleostei as the crestfishes, oarfish, opahs and ribbonfishes...
or Myctophiformes
Myctophiformes
Myctophiformes is an order of ray-finned fish consisting of two families of deep-sea marine fish, most notably the highly abundant lanternfishes...
, which are also usually treated as monotypic superorders – to the taxa mentioned before is still not well resolved at all, and regardless whether one calls them Protacanthopterygii sensu lato or Euteleostei, the phylogeny of this group of moderately-advanced Teleostei is in need of further study.
The ancestral Stomiiformes probably had thin brownish bodies, rows of egg-shaped 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 adorning the lower body parts, and mouths with numerous teeth. From these, two lineages evolved, probably some time during the Late Cretaceous
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
: Among the modern Stomiiformes, the Gonostomatidae
Gonostomatidae
Gonostomatidae is a family of deep-water marine fish, commonly named bristlemouths, lightfishes or anglemouths. It is a relatively small family, containing only eight known genera and 32 species...
and Phosichthyidae
Phosichthyidae
Lightfishes are small stomiiform fishes in the family PhosichthyidaeThey are very small fishes found in oceans throughout the world: most species grow no longer than 10 cm, while those in the genus Vinciguerria only reach 4 cm or so....
are phenetically very similar, but this is due to their being very plesiomorphic and retaining many traits of the original stomiiforms. Each of the two has characteristic synapomorphies with one of the more advanced stomiiform families – the Sternoptychidae
Sternoptychidae
The marine hatchetfishes or deep-sea hatchetfishes as well as the related bottlelights, pearlsides and constellationfishes are small deep-sea bathypelagic ray-finned fish of the stomiiform family Sternoptychidae...
and the Stomiidae
Stomiidae
Stomiidae is a family of deep-sea ray-finned fish, including the barbeled dragonfishes, stareaters and loosejaws.Stomiids are generally elongated fish with black or near-black bodies, but they are highly variable in form, and are sometimes grouped into multiple different families as a result. The...
, respectively. These two, in turn, are highly autapomorphic, and at a casual glance do not look as if they were as closely related to the other stomiiforms as they actually are.
Thus, the classification of the suborders and families
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
of the Stomiiformes is:
- Suborder Gonostomatoidei
- Family GonostomatidaeGonostomatidaeGonostomatidae is a family of deep-water marine fish, commonly named bristlemouths, lightfishes or anglemouths. It is a relatively small family, containing only eight known genera and 32 species...
– bristlemouths, anglemouths, "lightfishes" (including Diplophidae) - Family SternoptychidaeSternoptychidaeThe marine hatchetfishes or deep-sea hatchetfishes as well as the related bottlelights, pearlsides and constellationfishes are small deep-sea bathypelagic ray-finned fish of the stomiiform family Sternoptychidae...
– marine hatchetfishes, bottlelights, constellationfishes, pearlsides
- Family Gonostomatidae
- Suborder Phosichthyoidei
- Family PhosichthyidaePhosichthyidaeLightfishes are small stomiiform fishes in the family PhosichthyidaeThey are very small fishes found in oceans throughout the world: most species grow no longer than 10 cm, while those in the genus Vinciguerria only reach 4 cm or so....
– lightfishes - Family StomiidaeStomiidaeStomiidae is a family of deep-sea ray-finned fish, including the barbeled dragonfishes, stareaters and loosejaws.Stomiids are generally elongated fish with black or near-black bodies, but they are highly variable in form, and are sometimes grouped into multiple different families as a result. The...
– barbeled dragonfishes, loosejaws, stareaters
- Family Phosichthyidae