These are not very easy species to acclimatize. It is possible to keep one small
specimen at most, which will often live away from the light. They are herbivores
that sift the substrate looking for algae to eat. In among the prickles it is possible
to see the articulated pedicellariae, which end either in a tiny pincer for trapping
food or a sucker. The latter allows sea urchins to develop on rigid supports or
the glass sides of the tank.
Some species of sea urchins with varying sizes of prickles
can be found in marine aquariums.
These are not recommended for a marine invertebrate tank, as they attack other
species, such as sponges. Starfish are in fact either carnivorous, gripping their
prey with their long arms that emerge from a central disc, or microphages, in which
case they feed on small organisms on the bed.
The ophiuroids, sometimes called brittlestars and closely related to starfish,
have articulated arms which allow them to move around quite quickly. These arms,
like those of the starfish, can regenerate themselves if they break off.