Species Profile – Crinoids
Crinoids, also known as sea lilies or feather-stars, are marine echinoderms of the class Crinoidea. The name comes from Greek for “lily-like” in reference to their resemblance to a flower. They have a cup-shaped body (called a theca) with five or more feathery arms (rays) and, in some species, a segmented stalk for attachment to a surface. Theca and rays are together called the crown. The arms contain reproductive organs and sensory tube feet. Most of the body consists of an endoskeleton made up mainly of articulated series of calcareous pieces (ossicles) held together by connective tissues.
The majority of living crinoids are free-swimming and have only a vestigial stalk. The one we caught was one of the free-swimming species, known as comatulid crinoids. They swim by flapping their arms. They also have small curved “feet” called cirri that they use for movement. Once the animal finds a suitable perch, it uses its cirri to hold itself in place.
Crinoids are filter feeders. The tube feet are covered with a sticky mucous that traps tiny bits of organic matter suspended in the water. The food is then transported inward, down the length of the arms to the mouth.
There are only a few hundred known modern forms, but crinoids were much more numerous both in species and numbers in the past.