Most divers have had the pleasure of encountering at least a few starfish at various dive sites around the world; many of the starfish you may have seen are probably Brittle Stars. In a variety of shapes, sizes, and colors, these spiny members of the echinoderm family comprise approximately 1,900 known species, with new deep sea dwellers being discovered with some regularity.
Brittle Stars: The Basics
Not the same as starfish, but close relatives, brittle stars are also known as serpent stars, thanks to their long, whiplike arms. Some of the largest specimens have arms approximately two feet across, which when added to their central discs gives them a span of just over four feet. Most ophiuroids have five of these arms, which are equipped with water vascular systems for respiration, and tube feet for locomotion. While it can be hard to tell just where a starfish’s body begins and ends, there is a marked delineation between a brittle star’s body and its arms. The body tends to be roughly circular, and the disk, which contains all the animal’s organs, is easy to differentiate. While each leg has spines to allow prey to be captured and detritus to be gathered, the central disc usually has a smooth look.
Simple animals with a central nerve ring and nerves that extend along each arm, brittle stars have no eyes, but are equipped with light sensing organs as well as organs that can sense touch, and which can sense the presence of chemicals, allowing for a retreat if necessary.
Despite their name, Brittle Stars are actually quite flexible, and are capable of coiling an arm or two around an object and even clinging tightly to it after death has occurred. Their arms are muscular and serve as a means of locomotion as well as a means of transporting food to the mouth, which is located on the central disc’s underside.
Some brittle stars release clutches of eggs that hatch at a later time, while others have egg pouches where they keep their eggs safe until hatching time, when the young stars are released into the surrounding area. These little larvae usually have at least eight arms equipped with cilia that allow them to swim, and tiny suction cups that allow them to cling to rocks and plants. They grow slowly, reaching sexual maturity at about 2 years of age and reaching full size another two to three years later. When left undisturbed, most brittle star species can live for five years, with some species living much longer.
Brittle stars are found throughout the world, mostly preferring rocky reef areas where they can find shelter. While you’ll find small specimens in fairly shallow water and even in tide pools, most large brittle stars can be found at depths beyond 30 feet. In colors like aquamarine, black, red, and bright cerulean blue, these animals are a favorite with photographers.
The main threat to brittle stars is loss of habitat. While some are caught and used in the shell trade, they are less threatened by this activity than are starfish, thanks to their fragile nature. By focusing on caring for our oceans, we can protect them and their reef-dwelling neighbors, for future generations to enjoy.