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

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

angelshark Angel sharks are sharks belonging to the genus ''Squatina''. They are the only living members of the family Squatinidae and order Squatiniformes. They commonly inhabit sandy seabeds close to in depth. ''Squatina'' and other Squatiniformes d ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Squatinidae Squatiniformes is an order of sharks belonging to Squalomorphi. It contains only a single living genus ''Squatina'', commonly known as angelsharks. The oldest genus of the order, ''Pseudorhina'' is known from the Late Jurassic of Europe. Three oth ...

, 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 Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

. 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 margi ...

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

ray Ray or RAY may refer to: Fish * Ray (fish), any cartilaginous fish of the superorder Batoidea * Ray (fish fin anatomy), the bony or horny spine on ray-finned fish Science and mathematics * Half-line (geometry) or ray, half of a line split at an ...

-like shape and a well-developed tail and

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

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

barbels In fish anatomy and turtle anatomy, a barbel is a slender, whisker like sensory organ near the mouth (sometimes called whiskers or tendrils). Fish that have barbels include the catfish, the carp, the goatfish, the hagfish, the sturgeon, the z ...

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 on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

bases and a black leading margin on the underside of the

pectoral fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish aquatic locomotion, swim. Apart from the tail or caudal fin, fish fins have no direct connection with the vertebral column ...

s. The

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

(IUCN) has classified it as

Critically Endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...

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 that is responsible for scientific research and its commercial and industrial applications. CSIRO works with leading organisations arou ...

(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 designed to further the progress of science by disseminating new research findings to the scientific community. These journals serve as a platform for researchers, schola ...

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

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

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

landing site in central

Java Java is one of the Greater Sunda Islands in Indonesia. It is bordered by the Indian Ocean to the south and the Java Sea (a part of Pacific Ocean) to the north. With a population of 156.9 million people (including Madura) in mid 2024, proje ...

, was designated the

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

. The

specific epithet In Taxonomy (biology), taxonomy, binomial nomenclature ("two-term naming system"), also called binary nomenclature, is a formal system of naming species of living things by giving each a name composed of two parts, both of which use Latin gramm ...

comes from the

Greek Greek may refer to: 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 of all kno ...

''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 () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis, based on

mitochondrial DNA Mitochondrial DNA (mtDNA and mDNA) is the DNA located in the mitochondrion, mitochondria organelles in a eukaryotic cell that converts chemical energy from food into adenosine triphosphate (ATP). Mitochondrial DNA is a small portion of the 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 ...

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

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

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 (, ) is an Indonesian Provinces of Indonesia, province on the western part of the island of Java, with its provincial capital in Bandung. West Java is bordered by the province of Banten and the country's capital region of Jakarta to t ...

, Cilacap in

Central Java Central Java (, ) is a Provinces of Indonesia, 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 Yogya ...

, Kedonganan in

Bali Bali (English:; Balinese language, Balinese: ) is a Provinces of Indonesia, 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 o ...

, 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, habitat refers to the array of resources, 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 manifestation of its ...

is unavailable, though it is probably

bottom-dwelling The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

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 * Pectora ...

and

pelvic fin Pelvic fins or ventral fins are paired fins located on the ventral (belly) surface of fish, and are the lower of the only two sets of paired fins (the other being the laterally positioned pectoral fins). The pelvic fins are homologous to the hi ...

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 spiracles. 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 c ...

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 c ...

. 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 moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported o ...

. The tail is rather long, with the

caudal peduncle Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

moderately flattened and expanded laterally into

keel The keel is the bottom-most longitudinal structural element of a watercraft, important for stability. On some sailboats, it may have a fluid dynamics, hydrodynamic and counterbalancing purpose as well. The keel laying, laying of the keel is often ...

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 scale (zoology), scales, which can also provide effective Underwater camouflage, camouflage through the us ...

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 "bridging" form of reproduction between egg-laying oviparous and live-bearing viviparous reproduction. Ovoviviparous animals possess embryos that develop inside eggs that rema ...

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 o ...

longlines 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 grounds). Commercial fisheries include wild fisheries and fish farm ...

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

by the

IUCN The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the status ...

References

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