Brittle Stars and Basket Stars Echinoderms with Inflexible Arms

Like sea stars, brittle stars and basket stars have (in most species) five arms (which in some species are highly branched). But the arms of brittle stars and basket stars differ from those of star fish in that their central disk is easily distinguished from their arms (in starfish, the arms blend with the central disk such that it is difficult to see exactly where the two meet).

Brittle stars are so named because their arms can only move side to side and not up and down. If their arm is forced either up or down, it breaks. The lateral arm movements used by brittle stars and basket stars enables them to crawl across the substrate or cling to surfaces. There are about 2000 species of brittle stars and basket stars and they exhibit a range of feeding methods from filter feeding to scavenging to predation.