Ophiocanops fugiens

Ophiocanops fugiens is a living brittle star species belonging to the family Ophiocanopidae. For a time, it was thought to be the only living species in that family, but newer research has identified three other specimens of Ophiocanops that are quite distinct from O. fugiens.

Some scientists consider it the most primitive brittle star, similar to ancient Paleozoic forms, though others disagree. Its classification is heavily debated: it is often placed in the order Oegophiurida (suborder Zeugophiurina), or treated as a genus incertae sedis, or even given its own subclass, Oegophiuridea. Recent evidence hints at a relationship with the living family Ophiomyxidae, which would put it in the order Phrynophiurida.

Characteristics

The body of Ophiocanops fugiens is a central, armored, disk-shaped structure, clearly separated from the arms, and measures about 3 mm across. Like other brittle stars, its long, flexible arms move in a snake-like motion to propel it through water—hence the nickname "snake stars." These arms reach 35–40 mm in length and are roughly 1 mm wide. They are highly mobile, supported by an internal skeleton of calcium carbonate plates that resemble vertebrae and are called vertebral ossicles, controlled by the star's muscles.

Calcium carbonate plates also cover the body and arms, likely for defense, and the arms bear delicate spines. The arms lack dorsal and ventral shields, and the madreporite sits on the edge of the central disc. Digestive glands extend into the base of the arms.

There are no bursae for gonads or gas exchange and excretion. The mouth is small, triangular, and plated, with six conical teeth arranged in a circle. Reported colors include dark brown or purple, sometimes with spots.

Ecology

Once thought extinct, Ophiocanops fugiens is found in South Asian seas, with studied specimens collected off the shores of the Philippines. It lives in waters ranging from the seashore floor down to depths of 200 meters. It has a mutualistic symbiotic relationship with black corals.

It feeds on potentially harmful microorganisms and microparticles in coral reefs, and may also scavenge the benthic floor for detritus and plankton, or use the propulsive motion of its arms to capture particles. The arms also contain photoreceptive tissues that detect and respond to changes in light, since the species lacks eyes. No sexual dimorphism has been reported.