A robust, wholly black brittle star - disc and arms alike, without banding or pattern, which alone separates it from most others on the reef. The five arms are stout for the group and lined with short blunt spines standing out at right angles, the texture behind erinaceus, Latin for hedgehog. Arm span reaches about 15 cm (6 in), with a disc of 2 to 3 cm. Juveniles can show faint mottling that fades with age.
It lives packed under boulders, coral slabs and rubble on reef flats and shallow slopes to about 20 m (65 ft), often several animals sharing one stone with arms interlaced. Feeding is nocturnal and unfussy: detritus, organic film, carrion and small invertebrates, gathered by the arms and passed to the mouth. This is the brittle star most often turned up by lifting a rock on a 🌊 Red Sea reef flat, and the animals react to daylight immediately, pouring back into cover within seconds - which is a good reason to replace the stone the moment they start moving. Arms detach when grabbed and regrow, and the tube feet along their undersides carry light-sensitive cells, so the animal registers a torch beam without having eyes at all.
- uniformly black, disc and arms alike
- arms stout, covered in short blunt spines
- several animals packed under the same slab
