Echinoidea
Class Echinoidea is the sea urchins. The endoskeleton forma a round, rigid, test with moveable spines and pedicellariae. Urchins move by the moveable spines, jointed to sockets in the test and the sucker tipped tube feet. The flat and radiating body plan of sea stars can be transformed into that of a sea urchin by dropping the arms and pulling the oral and aboral surfaces to form a sphere. The five rows of ambulacral grooves and their tube feet now extend along the outer surface of the sphere. The mouth is on the bottom and the anus on the top.
Sea urchins graze on seaweed and sea grasses. In the process, they also ingest detritus and encrusting animals such as sponges and bryozoans. The mouth has an intricate system of jaws and muscles called Aristotle's lantern. It is used to bite off algae and other bits of food from the sea floor surfaces.
Heart urchins and sand dollars are in the class Echinoidea but have flattened bodies and short spines. They are deposit feeders that use their tube feet and soemtimes strands of mucus to pick up organic particles.
Sea urchins graze on seaweed and sea grasses. In the process, they also ingest detritus and encrusting animals such as sponges and bryozoans. The mouth has an intricate system of jaws and muscles called Aristotle's lantern. It is used to bite off algae and other bits of food from the sea floor surfaces.
Heart urchins and sand dollars are in the class Echinoidea but have flattened bodies and short spines. They are deposit feeders that use their tube feet and soemtimes strands of mucus to pick up organic particles.