Abyssobrotula galatheae
Encyclopedia
Abyssobrotula galatheae is a 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...

 of cusk eel in the family Ophidiidae
Ophidiidae
The cusk-eels family are a group of marine bony fishes in the order Ophidiiformes. The scientific name is from Greek ophis meaning "snake", and refers to their eel-like appearance...

, and the only species in its genus. It is the deepest-living 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...

 known; one specimen, trawled from a depth of 8,370 m (27,453 ft) in the Puerto Rico Trench
Puerto Rico Trench
The Puerto Rico Trench is an oceanic trench located on the boundary between the Caribbean Sea and the Atlantic Ocean. The trench is associated with a complex transition between the subduction zone to the south along the Lesser Antilles island arc and the major transform fault zone or plate boundary...

 in 1970, holds the record for the deepest fish ever captured. The first examples of this fish were misidentified by Staiger as Bassogigas profundissimus, before being described as a new species by Jørgen Nielsen in 1977. The species name refers to the research ship Galathea, which captured the first specimens.

Though uncommon, this species is known from the tropical and subtropical waters of all ocean
Ocean
An ocean is a major body of saline water, and a principal component of the hydrosphere. Approximately 71% of the Earth's surface is covered by ocean, a continuous body of water that is customarily divided into several principal oceans and smaller seas.More than half of this area is over 3,000...

s. It occurs in the abyssal
Abyssal zone
The abyssal zone is the abyssopelagic layer or pelagic zone that contains the very deep benthic communities near the bottom of oceans. "Abyss" derives from the Greek word ἄβυσσος, meaning bottomless. At depths of 4,000 to 6,000 metres , this zone remains in perpetual darkness and never receives...

 and hadal zone
Hadal zone
The hadal zone , also known as the hadopelagic zone and trench zone, is the delineation for the deepest trenches in the ocean...

s below a depth of 3,110 m (10,203 ft). It is bottom-dwelling in nature, although one individual has been captured from the water column in the Gulf of Panama
Gulf of Panama
The Gulf of Panama is a gulf in the Pacific Ocean, near the southern coast of Panama. It has a maximum width of , a maximum depth of and the size of . The Panama Canal connects the Gulf of Panama with the Caribbean Sea and the Atlantic Ocean...

. Its diet consists of polychaete worms and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s, such as isopods and amphipods. Reproduction is oviparous, possibly with pelagic eggs floating in a gelatin
Gelatin
Gelatin is a translucent, colorless, brittle , flavorless solid substance, derived from the collagen inside animals' skin and bones. It is commonly used as a gelling agent in food, pharmaceuticals, photography, and cosmetic manufacturing. Substances containing gelatin or functioning in a similar...

ous mass as in other members of the family.

A. galatheae has a short head
Head
In anatomy, the head of an animal is the rostral part that usually comprises the brain, eyes, ears, nose and mouth . Some very simple animals may not have a head, but many bilaterally symmetric forms do....

 with a downward inflection, a swollen snout
Snout
The snout, or muzzle, is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw.-Terminology:The term "muzzle", used as a noun, can be ambiguous...

, and an inferior
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...

 mouth
Mouth
The mouth is the first portion of the alimentary canal that receives food andsaliva. The oral mucosa is the mucous membrane epithelium lining the inside of the mouth....

. The body is soft, with a tapering tail
Tail
The tail is the section at the rear end of an animal's body; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds...

 and loose, transparent skin
Skin
-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

. Both the body and the head are covered with 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. The teeth are small and pointed, arranged in irregular rows; the two median and single pair of basibranchial (on the most ventral gill arch) tooth patches are distinctive for this species. The eyes are tiny, deep-set, and hidden. They are unlikely to be functional, but there is a well-developed system of sensory pores on its head. The lateral line
Lateral line
The lateral line is a sense organ in aquatic organisms , used to detect movement and vibration in the surrounding water. Lateral lines are usually visible as faint lines running lengthwise down each side, from the vicinity of the gill covers to the base of the tail...

 is only visible on the frontmost part of the body and lacks developed pores.

Externally, A. galatheae can be distinguished from other deep-sea ophidioids by its long pectoral fins, which contain only 10-11 fin rays each, and its flat, weakly developed opercular
Operculum (fish)
The operculum of a bony fish is the hard bony flap covering and protecting the gills. In most fish, the rear edge of the operculum roughly marks the division between the head and the body....

 spine
Spine (zoology)
A spine is a hard, thorny or needle-like structure which occurs on various animals. Animals such as porcupines and sea urchins grow spines as a self-defense mechanism. Spines are often formed of keratin...

. The long 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 anal fins contain 97-116 and 76-96 rays respectively. The pelvic fins and caudal fin are small and contain 2 and 8 rays respectively. The coloration is yellowish; the branchial cavity
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

 is black and the peritoneum
Peritoneum
The peritoneum is the serous membrane that forms the lining of the abdominal cavity or the coelom — it covers most of the intra-abdominal organs — in amniotes and some invertebrates...

 dark brown. The skeleton
Skeleton
The skeleton is the body part that forms the supporting structure of an organism. There are two different skeletal types: the exoskeleton, which is the stable outer shell of an organism, and the endoskeleton, which forms the support structure inside the body.In a figurative sense, skeleton can...

 is well-ossified, consistent with a benthic lifestyle; there are 18-21 precaudal vertebrae. It grows to at least 16.5 cm (6.5 in) long.
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