The hammerjaw, ''Omosudis lowii'', is a small

deep-sea The deep sea is broadly defined as the ocean depth where light begins to fade, at an approximate depth of 200 metres (656 feet) or the point of transition from continental shelves to continental slopes. Conditions within the deep sea are a combin ...

aulopiform Aulopiformes is a diverse 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 u ...

fish Fish are aquatic, craniate, gill-bearing 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. Approximately 95% of li ...

, found worldwide in tropical and temperate waters to 4,000 m (13,000 ft) depth. It is the only representative of its

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

, Omosudidae (from the

Greek Greek may refer to: Greece 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 ...

''omo'', "shoulder", and

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

''sudis'', either "esox, fish of the

Rhine ), Surselva, Graubünden, Switzerland , source1_coordinates= , source1_elevation = , source2 = Rein Posteriur/Hinterrhein , source2_location = Paradies Glacier, Graubünden, Switzerland , source2_coordinates= , so ...

" or "stake").

Description

The large head is dominated by a massive, truncated lower

jaw The jaw is any opposable articulated structure at the entrance of the mouth, typically used for grasping and manipulating food. The term ''jaws'' is also broadly applied to the whole of the structures constituting the vault of the mouth and serv ...

and large, high-set

eye Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and conv ...

s. The lower jaw has a dark, almost black distal end, "chin". The lower jaw possesses at least one pair of oversized, transparent, and dagger-like

teeth A tooth ( : teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

; the

palatine A palatine or palatinus (in Latin; plural ''palatini''; cf. derivative spellings below) is a high-level official attached to imperial or royal courts in Europe since Roman times.

s possess 1–4 pairs of slightly smaller teeth. The body itself is scaleless and laterally compressed; it is covered in

iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...

, silvery-gray

guanine Guanine () ( symbol G or Gua) is one of the four main nucleobases found in the nucleic acids DNA and RNA, the others being adenine, cytosine, and thymine (uracil in RNA). In DNA, guanine is paired with cytosine. The guanine nucleoside is called ...

with the dark

peritoneum The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesoth ...

peeking through in places. Dark smoky gray dorsally, the body tapers strongly towards a thin

caudal peduncle Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

(which has a dermal keel) and deeply forked

caudal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

. The

is a smoky black color, darker than the body and tail. All fins are

spine Spine or spinal may refer to: Science Biology * Vertebral column, also known as the backbone * Dendritic spine, a small membranous protrusion from a neuron's dendrite * Thorns, spines, and prickles, needle-like structures in plants * Spine (zoolog ...

less; both the low-slung

pectoral fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as ...

s (with 11–16 soft rays) and abdominal

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral surface of fish. The paired pelvic fins are homologous to the hindlimbs of tetrapods. Structure and function Structure In actinopterygians, the pelvic fin consists of two en ...

s (with eight soft rays) are fairly small. The single

dorsal fin A dorsal fin is a fin located on the back of most marine and freshwater vertebrates within various taxa of the animal kingdom. Many species of animals possessing dorsal fins are not particularly closely related to each other, though through conv ...

(with 9–12 soft rays) and

anal fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as se ...

(14–16 soft rays) are roughly equal in size; the anal fin's origin lies immediately posterior to the dorsal. The

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 epithelial ...

is uninterrupted and the

gill raker Gill rakers in fish are bony or cartilaginous processes that project from the branchial arch (gill arch) and are involved with suspension feeding tiny prey. They are not to be confused with the gill filaments that compose the fleshy part of the ...

s number 20–25. Like other members of their

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

, hammerjaws also possess a small

adipose fin Fins are distinctive anatomical features composed of bony spines or rays protruding from the body of a fish. They are covered with skin and joined together either in a webbed fashion, as seen in most bony fish, or similar to a flipper, as s ...

. The largest recorded hammerjaw measured 23 cm (9 inches) standard length (excluding the caudal fin).

Life history

Very little is known of the hammerjaw's life history. It inhabits the

mesopelagic The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins ...

and bathypelagic zones down to 4,000 m and is never caught in large numbers. It is inferred from their sporadic capture and sleek morphology that hammerjaws are swift swimmers—capable of avoiding sampling nets. Hammerjaws appear to

spawn Spawn or spawning may refer to: * Spawn (biology), the eggs and sperm of aquatic animals Arts, entertainment, and media * Spawn (character), a fictional character in the comic series of the same name and in the associated franchise ** '' Spawn: Ar ...

year-round; like many other deep-sea aulopiform fish, they are

hermaphrodite In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many Taxonomy (biology), taxonomic groups of animals (mostly invertebrate ...

s. They are

carnivorous A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other sof ...

and feed on

squid True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...

and other

pelagic fish Pelagic fish live in the pelagic zone of ocean or lake waters—being neither close to the bottom nor near the shore—in contrast with demersal fish that do live on or near the bottom, and reef fish that are associated with coral reef ...

; in turn, hammerjaws are known prey of

lancetfish Lancetfishes are large oceanic predatory fishes in the genus ''Alepisaurus'' ("scaleless lizard") in the monogeneric family Alepisauridae. Lancetfishes grow up to in length. Very little is known about their biology, though they are widely di ...

and

tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: ...

References

* * * * McGrouther, M. (2004)
Hammerjaw, ''Omosudis lowei'', ''Australian Museum Online'', October 2005 version
{{Taxonbar, from=Q1573789 Omosudidae Fish described in 1887 Taxa named by Albert Günther