This is a collection of aptly-named animals. Brittle stars have very fragile-looking, worm-like arms and basket stars have a series of branching arms resembling a basket. Brittle stars and basket stars are echinoderms that belong to the Class Ophiuroidea, which contains thousands of species. These animals are sometimes referred to as ophiuroids.
These marine invertebrates are not 'true' sea stars, but have a similar body plan, with 5 or more arms arranged around a central disc. The central disk of brittle stars and basket stars is very obvious, since the arms attach to the disc, rather than joining to each other at the base like they do in true sea stars.
The central disk of brittle stars and basket stars is usually relatively small, under one inch, and the whole organism itself may be under an inch in size. The arms of some species can be quite long, though, with some basket stars measuring over 3 feet across when their arms are extended (Source: Coral Reefs: An Ecosystem in Transition). These very flexible animals can curl themselves into a tight ball when they are threatened or disturbed.
Depending on the species, basket stars and brittle stars may be predators, actively feeding on small organisms, or may filter-feed by filtering organisms from the ocean water. They may feed on detritus and small oceanic organisms such as plankton and small mollusks.
The mouths of brittle stars and basket stars are located on their underside. They have no anus, so wastes are also expelled through the mouth.