Brittle stars, an invertebrate species closely related to the sea star, have varied reproductive strategies. Different species spawn and brood, while most can reproduce asexually through cloning. More than 1,800 different species of brittle stars have been identified. They can be found in every ocean on the planet, at every depth.
What Are Brittle Stars?
Brittle stars, a type of echidnoderm, have five flexible, jointed arms attached to a disk-shaped body. The mouth and anus are on the bottom of the disk. They live in large groups around coral and rock formations on the ocean floor. Brittle stars use their arms to push themselves along. They also have tube feet along the bottoms of their arms that excrete an adhesive, enabling them to climb up the sides of rocks and fish tanks. If they lose an arm to a predator, they can regenerate a new one. Body size among species varies from 1/4 inch in diameter to almost 2 inches.
Spawning is the most common way brittle stars reproduce. Male and female brittle stars release sperm and eggs, respectively, into the water. Fertilized eggs develop into four-armed swimming larvae called ophioplutei. The tiny ophioplutei feed on plankton for a few weeks and go through a metamorphosis to become five-armed juvenile brittle stars. In what is known as their settling stage, the juveniles sink to the ocean floor.
Some species fertilize and brood their eggs in a special chamber inside the female's body until they reach the juvenile stage. The juveniles leave when they are approximately 2 millimeters in diameter and are able to crawl. Smaller species of brittle stars tend to brood more than the larger species.
Asexual Reproduction or Cloning
Brittle stars can reproduce asexually in two ways. 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. Brittle star juveniles can also reproduce during their settling stage. When metamorphosis is almost complete, the baby brittle stars lose their last two larval arms. Special tissue at the point of attachment creates new ophioplutei, which swim off to develop into brittle stars.
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