Bowmouth guitarfish

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.

The lower jaw has three protruding lobes that fit into corresponding depressions in the upper jaw. There are around 47 upper and 50 lower tooth rows arranged in winding bands; the teeth are low and blunt with ridges on the crown. The five pairs of ventral gill slits are positioned close to the lateral margins of the head.The body is deepest in front of the two tall and falcate (sickle-shaped) dorsal fins. The first dorsal fin is about a third larger than the second and originates over the pelvic fin origins. The second dorsal fin is located midway between the first dorsal and the caudal fin. The broad and triangular pectoral fins have a deep indentation where their leading margins meet the head. The pelvic fins are much smaller than the pectoral fins, and the anal fin is absent. …

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.

Parasites. Parasites documented from this species include the tapeworms Carpobothrium rhinei, Dollfusiella michiae, Nybelinia southwelli, Stoibocephalum arafurense, and Tylocephalum carnpanulatum, the leech Pontobdella macrothela, the trematode Melogonimus rhodanometra, the monogeneans Branchotenthes robinoverstreeti and Monocotyle ancylostomae, and the copepods Nesippus vespa, Pandarus cranchii, and P. smithii. There is a record of a Rhina ancylostomus being cleaned by bluestreak cleaner wrasses (Labroides dimidiatus).