Brittle stars have a small central disk but long, slender arms. These arms are used for feeding and to help the brittle star sense its environment. Brittle stars have a water vascular system, and their tube feet are filled with water. The water is brought into the body through the underside of the disc. Also within the central disk lie the organs, it doesn’t have a brain but comes with a large stomach, genitals, muscles, and a mouth that comes with 5 separate jaws.
A brittle star’s arms are supported plates made from calcium carbonate. These plates work together like ball and socket joints to give the brittle star’s arms flexibility. This gives these stars very flexible arms that can have a graceful movement that allows them to move quite quickly.
They don’t move using their feet like sea stars and urchins do, but move by wriggling their arms. When they move, one arm points the way forward, while the arms on either side coordinate the rest of the brittle star’s movements in a “rowing” motion so that the star moves forward.
If you ever get the chance to see them move, you will be quite surprised at how fast they can go, they look a lot like spiders, sea spiders.
Most spawn to reproduce. Male and female brittle stars release sperm and eggs, respectively, into the water. After fertilization, they first become 4 armed larvae. These tiny larvae feed on plankton for a few weeks and go through a metamorphosis to become 5 armed tiny juvenile brittle stars. In what is known as their settling stage, at this point, they sink to the ocean floor and begin life as brittle stars.
Some species brood their eggs in a chamber inside the female’s body until they reach the juvenile stage. The juveniles leave the brood pouch when they are about 2 mm in size, it seems that the smaller species of brittle stars brood more often than the bigger ones.
They can also reproduce asexually. When one or more arms and a portion of the central body break off, both pieces of the brittle star will grow new bodies and arms to form two animals.