Ophiuroidea Gray, 1840
There are approximately 2,000 species of Brittle Stars or “Serpent Stars.” The five or six arms of Brittle Stars are very thin and fragile, and may break when the Echinoderm is disturbed or handled. The arms of the Brittle Star are separate appendages attached to the small, disk-like body. (The arms of Starfish or Sea Stars are extensions of its body.)
Like those of its relative the Starfish, the arms of the Brittle Star have amazing regenerative powers. The creature can lose all five or six of its arms and the top half of its body, and still regrow all lost parts. When cut in half, a Brittle Star will grow into two whole new animals in about three months. — One species, Microphiopholis gracillina, can even cast off its disk when upset, and later regrow that central area.
Brittle Stars have one bottomside opening which functions as both mouth and anus.
Brittle Stars can use their tube feet in locomotion, but mainly they use their arms for swimming about. The tube feet on the arms are used as gills, and as surfaces for collecting food particles suspended in the sea water. The Basket Star, or Sea Basket, has five arms which branch out and subdivide again and again, creating a globular net by means of which the Basket Star captures, and holds to its mouth, its food.
Members of this subclass Ophiuroidea may be carnivores, suspension or deposit-feeders, or scavengers.
Besides the similarity of five or six snake-like arms, the appearance of different members of the Brittle Star family varies as to its color. Some have bands of color on their arms. Some Brittle Stars are black, yellow, rust-colored, light green or green, gray, brownish-gray, red, or bright orange. Eudistoma carolinense has a reddish-brown or tan disk, and white arms. Some species of Brittle Stars have red blood cells in their water vascular systems. The red corpuscles cause the animal's tube feet to appear red.
Another differentiating factor is the smooth or “bristly” appearance of the Star. Some species have an arm-spread of 30 inches across and others are much smaller. Some species, such as the Dwarf Brittle Star (Axiognathus squamatus), are bioluminescent.
Brittle Stars inhabit all deep oceans of the world, with some species living as far down as 20,000 feet. They may also burrow in soft sand or mud near shore, or live near rocks or in crevices. They are often found around pilings. The Smooth Brittle Star, Ophioderma brevispinum, is commonly found in shallow subtidal beds.