The Indonesian angelshark (''Squatina legnota'') is a rare

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

angelshark The angelsharks are a group of sharks in the genus ''Squatina'' of the family Squatinidae. They commonly inhabit sandy seabeds close to in depth. Many species are now classified as critically endangered by the International Union for Conservat ...

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 ...

Squatinidae, known only from a few specimens collected from fish landing sites in southern

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Guine ...

. It is thought to inhabit the deep waters of the

continental slope A continental margin is the outer edge of continental crust abutting oceanic crust under coastal waters. It is one of the three major zones of the ocean floor, the other two being deep-ocean basins and mid-ocean ridges. The continental margin ...

. Reaching at least long, this species has a flattened,

ray Ray may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), a bony or horny spine on a fin Science and mathematics * Ray (geometry), half of a line proceeding from an initial point * Ray (g ...

-like shape and a well-developed tail and

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 ...

. It is characterized by the absences of fringes on its nasal

barbels In fish anatomy and turtle anatomy, a barbel is a slender, whiskerlike sensory organ near the mouth. Fish that have barbels include the catfish, the carp, the goatfish, the hagfish, the sturgeon, the zebrafish, the black dragonfish and some ...

and thorns down the midline of its back, as well as by its relatively plain grayish-brown dorsal coloration with dark saddles beneath the

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 ...

bases and a black leading margin on the underside of the

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. The

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

(IUCN) has classified it as Critically Endangered due to significant fishing pressure.

Taxonomy and phylogeny

The Indonesian angelshark was described by

Commonwealth Scientific and Industrial Research Organisation The Commonwealth Scientific and Industrial Research Organisation (CSIRO) is an Australian Government agency responsible for scientific research. CSIRO works with leading organisations around the world. From its headquarters in Canberra, CSIRO ...

(CSIRO) researchers Peter Last and William White in a 2008 volume of the

scientific journal In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. Content Articles in scientific journals are mostly written by active scientists such as s ...

''Zootoxa'', based on specimens found at several

n fish landing sites. One of the specimens, a long female from the

Cilacap Cilacap Regency ( jv, ꦏꦨꦸꦥꦠꦺꦤ꧀ꦕꦶꦭꦕꦥ꧀, also spelt: Chilachap, old spelling: Tjilatjap, Sundanese: ) is a regency () in the southwestern part of Central Java province in Indonesia. Its capital is the town of Cilacap. C ...

landing site in central

Java Java (; id, Jawa, ; jv, ꦗꦮ; su, ) is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea to the north. With a population of 151.6 million people, Java is the world's List ...

, was designated the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several ...

. The

specific epithet In taxonomy, binomial nomenclature ("two-term naming system"), also called nomenclature ("two-name naming system") or binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, bot ...

comes 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 ...

''legnotos'' ("having a colored border"), in reference to the dark leading margins of the pectoral fins. Björn Stelbrink and colleagues' 2010

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis, based on

mitochondrial DNA Mitochondrial DNA (mtDNA or mDNA) is the DNA located in mitochondria, cellular organelles within eukaryotic cells that convert chemical energy from food into a form that cells can use, such as adenosine triphosphate (ATP). Mitochondrial D ...

, found that the

sister species In phylogenetics, a sister group or sister taxon, also called an adelphotaxon, comprises the closest relative(s) of another given unit in an evolutionary tree. Definition The expression is most easily illustrated by a cladogram: Taxon A and t ...

of the Indonesian angelshark is the

Taiwan angelshark The Taiwan angelshark (''Squatina formosa'') is an angelshark in the family Squatinidae. The Taiwan angelshark is one of four species of Squatina in the waters around Taiwan and Japan. It is a demersal, ray-like shark that grows to 1–2 meters ...

(''S. formosa''); the two were the closest genetically of all the species examined. The pair additionally formed a

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

with the Japanese angelshark (''S. japonica'') and the ocellated angelshark (''S. tergocellatoides''), both also Asian species.

Distribution and habitat

The known specimens of the Indonesian angelshark have come from fish landing sites at Palabuhanratu in

West Java West Java ( id, Jawa Barat, su, ᮏᮝ ᮊᮥᮜᮧᮔ᮪, romanized ''Jawa Kulon'') is a province of Indonesia on the western part of the island of Java, with its provincial capital in Bandung. West Java is bordered by the province of Banten ...

, Cilacap in

Central Java Central Java ( id, Jawa Tengah) is a province of Indonesia, located in the middle of the island of Java. Its administrative capital is Semarang. It is bordered by West Java in the west, the Indian Ocean and the Special Region of Yogyakarta in t ...

, Kedonganan in

Bali Bali () is a province of Indonesia and the westernmost of the Lesser Sunda Islands. East of Java and west of Lombok, the province includes the island of Bali and a few smaller neighbouring islands, notably Nusa Penida, Nusa Lembongan, and Nu ...

, and Tanjung Luar in

Lombok Lombok is an island in West Nusa Tenggara province, Indonesia. It forms part of the chain of the Lesser Sunda Islands, with the Lombok Strait separating it from Bali to the west and the Alas Strait between it and Sumbawa to the east. It is rou ...

. Therefore, specific information on its preferred natural

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

is unavailable, though it is probably bottom-dwelling in the deeper waters of the

Description

The largest known Indonesian angelshark specimen measured long. As in all angel sharks, it has a flattened body with greatly enlarged

pectoral Pectoral may refer to: * The chest region and anything relating to it. * Pectoral cross, a cross worn on the chest * a decorative, usually jeweled version of a gorget * Pectoral (Ancient Egypt), a type of jewelry worn in ancient Egypt * Pectoralis ...

and

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. The broad, flattened head has a very short, blunt snout and small, widely spaced eyes placed somewhat on top. The eyes are followed by much larger, crescent-shaped

spiracle Spiracle or spiraculum may refer to: * Spiracle (arthropods), opening in the exoskeletons of some arthropods * Spiracle (vertebrates), openings on the surface of some vertebrates * Spiraculum, a genus of land snails in family Cyclophoridae Cycl ...

s. The nostrils are large and preceded by well-developed flaps of skin that reach the mouth; each flap bears two prominent

, which are smooth rather than fringed. The capacious, gently curved mouth is placed at the front of the head. There are long, deep furrows extending from the mouth corners onto and away from the lower jaw. The teeth number around 18 rows in both jaws; each is small and dagger-like, with a single sharp cusp. The five pairs of

gill slit Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of cartilaginous fish such as sharks and rays, as well as deep-branching vertebrates such as lampreys. In con ...

s are long and placed on the sides of the head. The pectoral fins are angular, with the anterior lobes of their bases free from the head, and their outer tips forming an angle of slightly under 120°. The tips of the pelvic fins are rounded; males have thick

claspers In biology, a clasper is a male anatomical structure found in some groups of animals, used in mating. Male cartilaginous fish have claspers formed from the posterior portion of their pelvic fin which serve to channel semen into the female's ...

. The two

s are close in shape and size, with rounded to angular apexes and slightly convex trailing margins. The first dorsal originates over the pelvic fins rear tips, and the second dorsal is placed close to the first. There is no

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 ...

. The tail is rather long, with the

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 ...

moderately flattened and expanded laterally into

keel The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...

s. The lower lobe of the short and triangular

is larger than the upper, and there is a notch in the upper lobe trailing margin. The dorsal surface is covered by small, roughly conical

dermal denticle A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales, which can also provide effective camouflage through the use of reflection and colouration, as we ...

s. This species is grayish brown above, darkening around the eyes and on the snout and becoming translucent at the trailing fin margins. There are blackish saddle markings below the dorsal fin bases, and sometimes also large, dark blotches and "eyespots" scattered over the dorsal surface. The underside is almost completely white, with a black leading margin on the pectoral fins.

Biology and ecology

Little is known of the Indonesian angelshark's natural history. It is presumably

aplacental viviparous Ovoviviparity, ovovivipary, ovivipary, or aplacental viviparity is a term used as a "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop insi ...

like other members of its family. The smallest male specimen, an adult, measured long.

Human interactions

The Indonesian angelshark is rarely caught incidentally on

demersal The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer of ...

longline Long line or longline may refer to: *''Long Line'', an album by Peter Wolf *Long line (topology), or Alexandroff line, a topological space *Long line (telecommunications), a transmission line in a long-distance communications network *Longline fish ...

s and marketed for meat and fins. If the presently limited Indonesian deepwater

fisheries Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life; or more commonly, the site where such enterprise takes place ( a.k.a. fishing ground). Commercial fisheries include wild fisheries and fish farms, both ...

were to expand, this species may be threatened as other angel shark species have shown themselves to be particularly susceptible to fishing depletion. As of 2020, the species is classified as Critically Endangered by the

IUCN The International Union for Conservation of Nature (IUCN; officially International Union for Conservation of Nature and Natural Resources) is an international organization working in the field of nature conservation and sustainable use of natu ...

References

{{DEFAULTSORT:angelshark, Indonesian Indonesian angelshark Fish of Indonesia Indonesian angelshark