Ringed Brittle Star

Ringed Brittle Star, Ophionereis annulata

The Ringed Brittle Star, Ophionereis annulata, is an Echinoderm and a member of the Ophiuroidea Class and the Cidaridae Family. In Mexico they are known as estrella frágil anillado. The Echinoderms are a phylum of marine animals which include Brittle Stars, Sea Cucumbers, Sea Lilies, Starfish and Urchins that are of great scientific interest because, via fossil records, they date to the Cambrian Age (over 500 million years ago) with 7,000 living species and 13,000 extinct ones. Globally there are 2,000 known species of Brittle Stars. They are agile relatives of the sluggish sea stars with anatomical structures that include a disk and five slender arms. They have five triangularly shaped jaws that frame a centrally placed mouth which is found on the ventral side. The arms are used for locomotion as they can rapidly “row” or pull themselves along the ocean floor. Brittle stars owe their name to the notorious capability of voluntarily severing arms which occurs as a self defense mechanism while under attack by predators. Complete regeneration of missing parts takes from two and eight weeks. Brittle Stars feed via either the absorption of nutrients through the skin or via the collection of particles with their arms which they transport to the mouth. They lack eyes and are concealed during the day hiding under rocks. They come out at night and are extremely active. They are preyed upon by crabs, fishes, sea stars, shrimps and other brittle stars. Brittle stars have never been an important item of human commerce. The Ringed Brittle Star is black and white in color with a disc that is covered with small overlapping scales which increase in size towards the edges that party cover the first arm plate. They have long and slender arms with three spines on each lateral arm plate. The arms are banded on both the dorsal and ventral surfaces which is a key to identification. The arms are approximately six times longer than the diameter of the disk and they travel via “stepping” utilizing their tube feet rather than the entire arm. They reach a maximum size of 30 cm (12 inches) and are found under rocks and crevices and on sponges, corals and sand within the intertidal zone up to water depths up to 90 feet. They are found in all Mexican waters of the Pacific and reported to be the most common Brittle Star within the Sea of Cortez.

Ringed Brittle Star, Ophionereis annulata. Collected from under rocks within tidal pools at Km 17, El Tule, Baja California Sur, February 2011. Size 15 cm (5.9 inches).