The slender sawtail catshark (''Galeus gracilis'') is a little-known species of catshark, part of the family Scyliorhinidae, endemic to northern Australia. It is found over the continental slope in on water. Growing to long, this shark has a slim gray body with four dark saddle markings below the dorsal fins and on the caudal fin, as well as a prominent crest of enlarged

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 along the dorsal edge of the caudal fin. The slender sawtail catshark is not valued by

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 ...

but is taken as

bycatch Bycatch (or by-catch), in the fishing industry, is a fish or other marine species that is caught unintentionally while fishing for specific species or sizes of wildlife. Bycatch is either the wrong species, the wrong sex, or is undersized or juve ...

. The International Union for Conservation of Nature (IUCN) presently lacks enough information to assess its conservation status.

Taxonomy and phylogeny

Leonard Compagno and John Stevens described the slender sawtail catshark in a 1993 issue 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 ...

''Records of the Australian Museum''. They gave it 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 ...

''gracilis'', meaning "slender" in Latin; previously, the species had been provisionally termed ''Galeus'' sp. A. The type specimen is a long adult female, caught in January 1988 north of Melville Island, Northern Territory. Within the genus, ''G. gracilis'' appears to be closely related to '' G. eastmani'', '' G. longirostris'', and '' G. nipponensis''. A 2005 phylogenetic analysis, based on

mitochondrial A mitochondrion (; ) is an organelle found in the cells of most Eukaryotes, such as animals, plants and fungi. Mitochondria have a double membrane structure and use aerobic respiration to generate adenosine triphosphate (ATP), which is use ...

and nuclear DNA, reported that this species, ''G. eastmani'', and ''G. sauteri'' 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, ...

apart from ''G. melastomus'' and ''G. murinus''.

Description

A small species growing to at least long, the slender sawtail catshark has a slim body with a nearly cylindrical cross-section, and a short, narrow head with a rounded snout. The eyes are horizontally oval and equipped with rudimentary

nictitating membrane The nictitating membrane (from Latin '' nictare'', to blink) is a transparent or translucent third eyelid present in some animals that can be drawn across the eye from the medial canthus to protect and moisten it while maintaining vision. All ...

s (protective third eyelids). Below each eye is a thin ridge, and behind is a tiny

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 ...

. The nostrils are divided by small, triangular flaps of skin in front. The mouth forms a wide arch and bears moderately long furrows around the corners. The teeth are small and closely set, numbering 54–57 rows in the upper jaw and 54–62 rows in the lower jaw. Each tooth has a narrow central cusp usually flanked by one, occasionally two small cusplets on either side. The teeth of males are slightly larger and longer than those of females. There are five pairs of gill slits, with the fourth and fifth pairs over the pectoral fin bases. The first dorsal fin slightly exceeds the second in size and originates over the midpoint of the

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 ...

bases. The second dorsal fin is positioned over the last third of the

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 dorsal fins have rounded apexes. The short, wide pectoral fins are roughly triangular, with rounded corners. The pelvic and anal fins are long-based, low, and fairly angular. Adult males have long, tapering claspers, each with saw-like rows of denticles along the inner surface, and twisted tips. The anal fin base measures around 11% of the total length and exceeds or matches the distances between the anal fin and the pelvic and caudal fins. The caudal fin is narrow, with a small but distinct lower lobe and a ventral notch near the tip of the upper lobe. The body and fins are densely covered by tiny, overlapping

s. Each has a teardrop-shaped crown covered by small pits, and bears a central ridge and typically three marginal teeth. There is a crest of enlarged denticles along the front portion of the caudal fin dorsal margin. This species is light gray above and lighter below; there is a small, dark saddle below each dorsal fin base, as well as two more saddles on the caudal fin, the second of which almost forms a complete ring. Some sharks also have a faint darker blotch over each flank. The inner lining of the mouth is dark gray.

Distribution and habitat

Apparently rare, the slender sawtail catshark has been collected from off Cape Cuvier and Port Hedland in Western Australia, off Melville Island off Northern Territory, and off Cape York in Queensland. It may also be present in eastern Indonesian waters. It is unknown whether these scattered records represent separate populations or a single continuous population.

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 ...

in nature, this shark inhabits the continental slope at a depth of .

Biology and ecology

Virtually nothing is known of the slender sawtail catshark's natural history. Males

mature sexually Sexual maturity is the capability of an organism to reproduce. In humans it might be considered synonymous with adulthood, but here puberty is the name for the process of biological sexual maturation, while adulthood is based on cultural definiti ...

at a length of .

Human interactions

Unknown numbers of slender sawtail catsharks are caught incidentally by the Western Trawl Fishery operating off northwestern Australia. There is no direct fishing for this species as it has no commercial value. Given a lack of information on conservation threats, the International Union for Conservation of Nature (IUCN) has listed this species as

Data Deficient A data deficient (DD) species is one which has been categorized by the International Union for Conservation of Nature (IUCN) as offering insufficient information for a proper assessment of conservation status to be made. This does not necessaril ...

References

{{Taxonbar, from=Q980786

slender sawtail catshark The slender sawtail catshark (''Galeus gracilis'') is a little-known species of catshark, part of the family Scyliorhinidae, endemic to northern Australia. It is found over the continental slope in on water. Growing to long, this shark has a s ...

Marine fish of Northern Australia Marine fish of Western Australia