Rhina ancylostoma, Bloch & Schneider, 1801
Rhina ancylostomus, also known as the bowmouth guitarfish, shark ray, mud skate, or sharkfin skate, is a species of ray and a member of the family Rhinidae. Its evolutionary affinities are not fully resolved, though it may be related to true guitarfishes and skates. This rare species occurs widely in the tropical coastal waters of the western Indo-Pacific, at depths of up to 90 m (300 ft). Highly distinctive in appearance, Rhina ancylostomus has a wide and thick body with a rounded snout and large shark-like dorsal and tail fins. Its mouth forms a W-shaped undulating line, and there are multiple thorny ridges over its head and back. It has a dorsal color pattern of many white spots over a bluish gray to brown background, with a pair of prominent black markings over the pectoral fins. This large species can reach a length of 2.7 m (8.9 ft) and weight of 135 kg (298 lb).
Rhina ancylostomus is a heavily built fish growing to 2.7 m (8.9 ft) long and 135 kg (298 lb) in weight.
The head is short, wide, and flattened with an evenly rounded snout; the front portion of the head, including the medium-sized eyes and large spiracles, is clearly distinct from the body. The long nostrils are transversely oriented and have well-developed skin flaps on their anterior margins.
While uncommon, Rhina ancylostomus is widely distributed in the coastal tropical waters of the western Indo-Pacific. In the Indian Ocean, it is found from KwaZulu-Natal in South Africa to the Red Sea (including the Seychelles), across the Indian subcontinent and Southeast Asia (including the Maldives), to Shark Bay in Western Australia. Its Pacific range extends northward to Korea and southern Japan, eastward to New Guinea, and southward to New South Wales. Found between 3 and 90 m (10 and 300 ft) deep, this ray spends most of its time near the sea floor but can occasionally be seen swimming in midwater. It favors sandy or muddy habitats, and can also be found in the vicinity of rocky and coral reefs and shipwrecks.
Rhina ancylostomus is a strong swimmer that propels itself with its tail like a shark. It is more active at night and is not known to be territorial. This species feeds mainly on demersal bony fishes such as croakers and crustaceans such as crabs and shrimp; bivalves and cephalopods are also consumed. Its bands of flattened teeth allow it to crush hard-shelled prey. In contrast to previous observations, two R. ancylostomus examined in a 2011 stable isotope study were found to have fed on pelagic rather than demersal animals.
The tiger shark (Galeocerdo cuvier) is known to prey on Rhina ancylostomus. The ray is protected by the thorns on its head and back, and it may ram perceived threats.
Reproduction in Rhina ancylostomus is viviparous, with the developing embryos sustained to term by yolk. Adult females have two ovaries and two uterine horns. The litter size varies between two and eleven pups, and newborns measure 45–51 cm (18–20 in) long. Sexual maturity is attained at lengths of 1.5–1.8 m (4.9–5.9 ft) for males and over 1.8 m (5.9 ft) in females. Females grow larger than males.
Throughout its range, the bowmouth guitarfish is caught incidentally or intentionally by artisanal and commercial fisheries using trawls, gillnets, and line gear. The fins are extremely valuable due to their use in shark fin soup, and are often the only parts of the fish kept and brought to market. However, the meat may also be sold fresh or dried and salted, and it is highly sought after in India. When caught as bycatch in trawls, Rhina ancylostomus is considered a nuisance because its strength and rough skin make it difficult to handle, and as the heavy ray thrashes in the net it can damage the rest of the catch. In Thailand, the enlarged thorns of this species are used to make bracelets.
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