Known as the Feathertail stingray, Pastinachus sephen is a ray of the Dasyatidae family (order Rajiforme) that inhabits a large region of the Indo-Pacific waters, from the Red Sea in the west, to Japan to the north, and Australia to the east including Micronesia. Common in coastal waters up to 60 meters deep, they are associated with coral and/or sandy habitats. It is an amphidromous species, meaning that it has the capacity to inhabit both salt and fresh waters, and the choice of habitat is not conditioned by reproduction. There have been recorded specimens of Pastinachus sephen more than 2,000 km from the sea, in the Ganges river.
The body of Pastinachus sephen is formed by a rhomboid shaped disc in which the snout is rounded and ends in a blunt tip. The anterior margin of the disc is practically straight or slightly convex, and ends at the apexes of the pectoral fins, which acquire a rounded shape. Almost the entire surface of the disc is covered by wide bands of dermal denticles. These dermal denticles are absent in newborns, although they develop rapidly after birth. Pastinachus sephen has small eyes, quite separated from each other, behind which we find the spiracles, whose size is slightly larger than the diameter of the eyes. The mouth of the Feathertail stingray is located in ventral position, and inside it has teeth with hexagonal shape, which are distributed forming numerous rows. On the back of the animal, we find what is undoubtedly the most distinctive feature of this species, and is none other than its tail, which is equivalent to up to twice the length of the disc. The base of the tail is wide, although its diameter decreases along the first third of its length. At this height we find a spine, with its serrated edges, and which is associated with a toxin-producing gland. From the spine, the tail adopts a cylindrical and slender section. During the second third of the length of the tail, this one presents a very developed ventral cutaneous fold, whose height is equivalent to several times the thickness of the tail in this region. This skin fold or sail, is the main characteristic feature of Pastinachus sephen. Finally, the last third of the tail length is filamentous and lacks ventral skin fold.
The body coloration of this species on its dorsal side is light brown to black, while the ventral side is mostly white. The tip of the tail, as well as the ventral skin folds are of an intense black color. In juvenile specimens, we can observe 4 circles in the center of its disc, which tend to disappear as the specimens mature. The maximum total length, with its long tail, is 3 meters, of which 1.8 meters corresponds to the maximum length of the disc.
Pastinachus sephen is a mostly solitary species, although it has been described that when they enter shallow lagoons to rest, they can be grouped in small groups in order to increase their security against predators (sharks, especially hammerhead sharks, as well as dolphins). During the day it is the time when the individuals of this species are most active. We will usually observe them stirring the sandy bottoms in search of their prey, mainly crustaceans, molluscs and small fish. This is a very frightening species in general, it will quickly flee when it notices the presence of divers in its vicinity.
Its reproduction is ovoviviparous, and at the moment of giving birth, the young measure approximately 18 cm in diameter.
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