Brittlestars  can be found in nearly all marine environments, from polar to  tropical seas, and from the intertidal to the deep-sea. They are  often extremely numerous, but because they are cryptic, are difficult  to find. Ophiuroids do not generally inhabit unstable high energy  areas such as beaches. They are often found in lagoon environments,  burrowed in sand and mud. On tropical reefs, they are generally  hidden under rocks (especially during the day). Some species also  inhabit large sponges (with which they have a  mutualistic  relationship). Brittlestars can also be found in root holdfasts of  kelps or seagrasses. Ophiuroids are very common in the deep-sea. A  very few species can be found in estuarine, brackish water conditions.

Where are ophiuroids found?