many echinoderms eat microscopic particles of organic matter in the
seawater. They make water currents by beating their hair like cilia,
which moves particles along the food grooves to the mouth. The water
currents aid in a different way too. They bring a fresh supply of
water, rich in oxygen, to the surface gills for the echinoderms to
Let’s take a
look at some of the cousins. Let’s begin with the brittle star, which
belongs to a class called Ophiuroidea. Brittle stars look like
starfish, with longer, thinner arms and smaller disc-shaped bodies.
The most obvious
thing about sea cucumbers is that they look like cucumbers. They
belong to a class called Holothuroidea. They have no spine;
microscopic spicules in their skin support the body.
The sea cucumber has a peculiar habit. It
offers shelter to the pearl fish inside its body. It can take in
more than one pearl fish at a time inside its body. The pearl fish,
so called because of the pigment-dotted transparent body, gets
shelter and food from the sea cucumber; it eats the sea cucumber’s
internal organs. This, however, does not kill the protector, for the
sea cucumber is capable of regenerating the organs. The act is not
particularly beneficial to the sea cucumber either.