Porcupine ray

Appearance

The pectoral fin disc of the porcupine ray is evenly oval, almost as wide as long, and very thick at the center, giving it a domed appearance. The tip of the snout is rounded and barely protruding. The small eyes are closely followed by much larger spiracles. Between the narrow nostrils is a skirt-shaped curtain of skin; the posterior margin of the curtain is strongly fringed and overhangs the mouth. The mouth bears 3–5 papillae on the floor and prominent furrows at the corners. The area around the mouth, including the curtain, are heavily covered by more papillae. There are around 48 tooth rows in either jaw. The teeth are small and flattened. Five pairs of gill slits are located on the underside of the disc.

The pelvic fins are small and narrow. The thin, rapidly tapering tail is about equal to the disc in length and has an almost cylindrical cross-section, without fin folds. The tail also has no venomous stinging spine, unlike other members of the family. A dense patch of flattened, heart-shaped dermal denticles covers the center of the disc and extends onto the tail. Larger individuals additionally have numerous tall, sharp thorns over the entire upper surface of the disc. The porcupine ray is plain light to dark gray or brown above, darkening to blackish towards the tail tip, and white below. This large species grows to at least 1.2 m across and 2.2 m long, and may reach 1.5 m across.

Distribution

The porcupine ray is widely distributed, but uncommon compared to other stingrays that share its range. It is found all along the continental periphery of the Indian Ocean, from South Africa to the Arabian Peninsula to Southeast Asia to Ningaloo Reef off western Australia, including Madagascar, the Seychelles, and Sri Lanka; it has colonized the eastern Mediterranean Sea through the Suez Canal. In the Pacific Ocean, its range continues through Indonesia and New Guinea, north to the Philippines, east to the Gilbert Islands and Fiji, and south to Heron Island off eastern Australia. This species is also found in the eastern Atlantic Ocean off Senegal, Guinea, and Côte d'Ivoire. Bottom-dwelling in nature, the porcupine ray is found close to shore at depths of 1–30 m. It inhabits sandy flats, coral rubble, and seagrass beds, often near reefs, and also enters brackish water.

Behavior

The porcupine ray can sometimes be observed lying still on the bottom in the open or inside caves. It is known to form groups at Ningaloo Reef. Its diet consists primarily of sipunculids, polychaete worms, crustaceans, and bony fishes. When feeding it plows deeply into the bottom, expelling excess sediment from its spiracles in a plume visible from a long distance away. Parasites documented from this ray include the tapeworm "Rhinebothrium devaneyi", the nematode "Echinocephalus overstreeti", and the capsalid monogeneans "Dendromonocotyle urogymni" and "Neoentobdella baggioi". The porcupine ray is aplacental viviparous, with the developing embryos sustained to term by histotroph secreted by the mother. Mangrove forests serve as important habitat for juvenile rays. Males and females mature sexually at about 90 and 100 cm across respectively.