Smalleye Stingray

Appearance

The smalleye stingray has a distinctive shape among its family: the pectoral fin disc is more than 1.4 times wider than long, with the outer corners forming obtuse angles. The anterior margins of the disc are sinuous and converge on a rounded snout with a slightly projecting tip. The eyes are small and immediately followed by a pair of much larger spiracles. The mouth is wide and contains five papillae across the floor. The tail is not quite as long as the disc, and is broad and flattened from its base to the stinging spine. The tail spine of one specimen examined measured 9.1 cm long and bore 75 serrations. After the spine, the tail abruptly becomes thin and cylindrical, with a low, thick fin fold running underneath.

The upper surface of the disc is covered by many large dermal denticles with star-shaped bases, concentrated on the snout. This ray is brown to reddish brown above, darkening towards the tip of the tail, and white below, becoming slightly dusky at the fin margins and on the tail. The dorsal surface bears characteristic large white spots beside the eyes, around the disc center, and in a row on either side about two-thirds of the way to the pectoral fin tips. There is also a row of small white spots on either side of the tail base. One of the largest stingray species, the smalleye stingray can reach a disc width of 2.2 m and a total length of 3.2 m.

Distribution

The smalleye stingray is widely but possibly discontinuously distributed in the Indian and Pacific Oceans, having been reported from off Tofo in Mozambique, Malé in the Maldives, the coasts of India and Bangladesh, the Gulf of Thailand, Malaysia and Indonesia, the Arafura Sea, and possibly the Philippines. This species has been reported from inshore habitats and river mouths, including the Ganges River estuary, as well as from deeper water; it is uncertain which is its preferred habitat. At Tofo, smalleye stingrays have been seen swimming over reefs at a depth of 15–25 m, where the water temperature is 23–28 °C. Although it had been presumed to be bottom-dwelling, these observations of individuals in mid-water suggest that the smalleye stingray may in fact be semi-pelagic in nature.

Behavior

The disc shape of the smalleye stingray suggests that it may swim in a fashion unlike other stingrays and more akin to other rays with very broad pectoral fin discs, i.e., flapping its pectoral fins up and down rather than undulating the pectoral fin margins; this species would thus represent a case of convergent evolution with those ray families. Off Tofo, most individuals are accompanied by multiple cobia. A known parasite of this species is the tapeworm "Oncomegoides celatus", which infests the spiral valve intestine. As with other stingrays, the smalleye stingray is aplacental viviparous with the developing embryos being sustained by yolk and later histotroph secreted by the mother. There is a record of a female gestating a single late-term fetus, which exhibited the same spotted color pattern as the adult. Newborn rays likely measure 31–33 cm across.