The class called Crinoidea contains the marine feather stars. There are approximately 625 species of feather stars and like most echinoderm classes, crinoids are found in most oceans and at all depths. They are a strange sight to behold. A mass of bird feathers attached to a pin prick of a body is probably the best way to describe a crinoid. Feather stars were once one of the most prominent organisms on the planet. Today they are not uncommon and are a favourite subject of the underwater photographer because of their amazing shape and colours.
Group size range:
(3cm - 50cm)
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|What do they look like?
Feather stars are curious looking organisms. Their relationship to other echinoderms is not immediately obvious. They consist of a mass of feather like arms radiating from a tiny body. On this small body the mouth faces upward, opposite to other echinoderms. Feather stars have tube feet on their arms but these have no suckers at the end, unlike starfish and sea urchins. Feather stars come in a great range of colours including some bright yellows and reds that appear to advertise the presence of the feather star to all around them. As in other brightly coloured marine animals, the crinoid's bright colours may serve to remind fish and other predators of their poisonous nature.
|Where do they live?
Feather stars are found in oceans in the tropics, temperate and polar zones. They generally shelter by day under ledges and in caves and come out at night to feed. They are often found hanging under caves and overhangs by day. When nights falls, Feather stars migrate to the top of the reef or push their arms out into the currents usually present near dropoffs or at the entrance of caves. Here, they trap fine particles using their tube feet. Feather stars are usually solitary but may occur in small groups around their favourite haunts.
|How and what do they eat?
Feather stars are almost exclusively suspension feeders. They are referred to as passive suspension feeders because they do not generate feeding currents but rather rely on the external movement of water by their feeding arms. Compare this situation to other suspension or filter feeders like polychaete worms (go to the Phylum Annelida). Polychaete worms (Phylum Annelida) like Christmas Tree worms are called active suspension feeders because they use cilia to drive water currents through their feeding apparatus.
|What eats them?
Little is known about the predators of crinoids. Fish, as with other echinoderms, are probably the principle predators.
|How do they grow and reproduce?
Feather stars have separate sexes which are impossible to distinguish. [Note: need info on fertilisation here: external or internal or both?] In most species, larvae develop indirectly, meaning that they pass through one or more stages that look very little like the adult. In species with indirect development, the larvae are called vitellaria larva. These swim in the water column for 10-40 days (depending on the species and the temperature of the water) and eventually settle as baby feather stars. Thereafter, the feather star grows gradually to become an adult feather star, usually 8 –12 months later. Some species develop directly (have no different-looking larval stage) and are nourished during development by food in the egg supplied by the mother.
|Who do they live with?
Feather stars do not seem to form many symbiotic relationships.
|Their connection with people.
Feather stars have little commercial value and are generally not endangered. They are not eaten by any human culture.
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