Crinoidea or feather stars (sea lillies)
Sea lilies have two morphologies but only one is found in shallow water. Many deepwater crinoids are called stalked crinoids because the ring of feather looking arms is placed at the end of a long and thin articulated stalk on a structure called the calyx. Shallow water crinoids on the other hand have a series of hooks, the cirri, on the lower part of the calyx that helps then attach temporarily to the substrate. Then tend to hide during the day and climb in the current at night to capture plankton, although often in deeper water (15-20m), they remain extended during the day.
Crinoids have articulated arms with numerous lateral pinnules, each with a series of thin podia that form the distal part of the water vascular system, which unlike in the other classes of echinoderm is not connected to the outside water. At night, they extend their arms in the current and capture small particles in suspension in the water with their numerous podia. The food is then progressively brought to the mouth by cilia that cover the ambulacral groove.
When accidentally dislodged from their anchoring point, some crinoids are able to actively swim by undulating their extended arms in the water.
Although there are probably quite a few species, only three are described here as the identification of crinoids is difficult and based on fine structure of the skeletal elements.
Feather stars
