The longtail stingray reaches a maximum known disc width of, length of, and weight of. It has a diamond-shaped pectoral fin disc about a sixth wider than long, with the outer corners broadly rounded. The front margins are nearly straight, meeting the tip of the snout at a blunt angle. There is a row of five papillae across the floor of the mouth; the two on the sides are smaller than the others. The pelvic fins are rounded. The whip-like tail bears a stinging spine and measures more than twice as long as the disc. Behind the spine, the tail becomes laterally compressed with a low keel above and a short, narrow fin fold below. There is a row of pointed tubercles running along the midline of the back from between the "shoulders" to the base of the tail. Two much shorter rows of smaller tubercles, slightly converging backward, are found alongside the central row behind the shoulders. Numerous small dermal denticles are also found between the eyes and on the tail behind the spine. The dorsal coloration varies from plain reddish-brown to dark gray, and the underside is light. The extent of denticle coverage and number of oral papillae can vary among individuals. The longtail stingray closely resembles the diamond stingray, which is found in the same region, but can be distinguished by its lack of an upper tail fold. The length of the tail is not a reliable diagnostic character for this species, as it is frequently damaged.
Biology and ecology
Apparently solitary in nature, the longtail stingray is a predator of bottom-dwelling bony fishes and invertebrates, in particular stomatopods, decapods, and molluscs. Known parasites of this species include the tapeworms Acanthobothrium cimari, A. cleofanus, A. costarricense, A. puntarenasense, and A. vargasi, Anthocephalum lukei and A. michaeli, Parachristianella dimegacantha, Pseudochristianella elegantissima and P. nudiscula, and Pterobothrioides carvajali, and the monogenean Listrocephalos whittingtoni. Like other stingrays, the longtail stingray is aplacental viviparous with the developing embryos sustained initially by yolk and later by histotroph produced by the mother. Adult females have a single functional ovary. Near-term females appear to swim into shallow estuaries and tidal creeks to give birth, following a gestation period of 10-11 months, and may mate again immediately after. A litter contains 1-5 young, each measuring about across. Males mature sexually at across, and females at across.
Human interactions
The tail spine of the longtail stingray is potentially dangerous to humans. This species is of some commercial importance in Mexico, where it is sold fresh or dried and salted. This species is likely landed by inshore fisheries targeting shark and ray throughout Central America; it is caught by bottom trawls and longlines, and is especially susceptible to gillnets as its tail spine easily becomes entangled in the mesh. The impact of fishing on its population is unknown, as fishery landings in the region are poorly monitored and the longtail stingray is not reported separately from other ray species. As a result, the International Union for Conservation of Nature has listed this species as Data Deficient, while noting that its slow reproductive rate would limit its capacity to recover from over-exploitation.
