Brittle and Basket Stars: Ophiuroidea

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BRITTLE AND BASKET STARS: Ophiuroidea

DWARF BRITTLE STAR (Amphipholis squamata): SPECIES ACCOUNTS
TROPICAL BRITTLE STAR (Ophiactis savignyi): SPECIES ACCOUNTS

PHYSICAL CHARACTERISTICS

Brittle and basket stars are sea animals that have long, thin, flexible arms. The bottom of the arms is covered with sucking tube feet. The arms of brittle stars are easily broken. The arms of both types of stars have a skeleton that looks like a string of small bones. Most brittle and basket stars have five arms, but a few species of brittle stars have six or seven arms. The arms of basket stars have as many as twenty branches. Basket stars are larger than brittle stars, their arms reaching a length of 28 inches (70 centimeters) and the body being as large as 6 inches (14 centimeters) across. The mouth of brittle and basket stars is on the bottom of the body and is framed by five jaws bearing spiny teeth. At the base of each arm are slits that are openings for pouches used for obtaining oxygen and, in some species, for releasing eggs and sperm.

GEOGRAPHIC RANGE

Brittle and basket stars live in all the oceans of the world.

HABITAT

Some brittle and basket stars burrow into muddy or sandy sea bottoms. Others live on or among algae, sponges, and coral. Algae (AL-jee) are plantlike growths that live in water and have no true roots, stems, or leaves.

DIET

Some brittle and basket stars eat sea animals, alive or dead. Others eat particles from the bottom or from the open water.

BEHAVIOR AND REPRODUCTION

Many brittle and basket stars move by powerful arm strokes that lift their bodies and thrust them forward. Other species slither along the bottom. Brittle stars are good climbers and can cling to rocks or coral above the sea floor. Brittle stars break off their arms or parts of their bodies to escape from predators. The lost body parts grow back.

Most brittle and basket stars have separate sexes. Eggs and sperm are released into the water through the slits at the bases of the stars' arms. After uniting with sperm, the eggs develop into larvae (LAR-vee), which are animals in an early stage that change form before becoming adults. The larvae drift freely in the water eating microscopic animals and then transform into young stars. In some species eggs that have united with sperm develop into larvae that do not feed and quickly transform into young stars. In other species the fertilized eggs develop directly into young stars.

Some species of brittle and basket stars make both eggs and sperm, and the eggs unite with sperm and develop in pouches at the bases of the female's arms. Other species use both sexual reproduction and asexual reproduction by splitting. Asexual (ay-SEK-shuh-wuhl) means without the uniting of egg and sperm for the transfer of DNA from two parents.

BRITTLE STARS, BASKET STARS, AND PEOPLE

Brittle and basket stars have no known importance to people.

WHAT'S IN A NAME?

Brittle stars and basket stars, sea lilies and feather stars, sea stars, sea daisies, sea urchins and sand dollars, and sea cucumbers all belong to the group of animals called echinoderms (ih-KYE-nuh-durhms), which means "prickly skin."

CONSERVATION STATUS

Brittle and basket stars are not considered threatened or endangered.

DWARF BRITTLE STAR (Amphipholis squamata): SPECIES ACCOUNTS

Physical characteristics: The body of dwarf brittle stars is only about 0.2 inches (5 millimeters) across, bluish or gray, circular, and covered with scales. The arms are short and thin and are orange, dark brown, beige, black, or gray.

Geographic range: Dwarf brittle stars live in all oceans of the world.

Habitat: Near the shore dwarf brittle stars live among algae, sea moss, and similar growths. In deep water they live under rocks and on sandy surfaces.

Diet: Dwarf brittle stars feed on particles such as algae and microscopic animals in the sand or mud and drifting in the water. One species feeds on dead fish.

Behavior and reproduction: Dwarf brittle stars are good climbers that use their tube feet when they move. They also use their tube feet to wipe food particles from their sticky spines. If bumped, dwarf brittle stars coil their arms over their body and sink rapidly to the bottom. Dwarf brittle stars make eggs and sperm at the same time. The eggs unite with sperm and develop in pouches at the base of the star's arms.

Dwarf brittle stars and people: Dwarf brittle stars have no known importance to people.

Conservation status: Dwarf brittle stars are not considered threatened or endangered. ∎

TROPICAL BRITTLE STAR (Ophiactis savignyi): SPECIES ACCOUNTS

Physical characteristics: Tropical brittle stars usually have six arms. The body is 0.04 to 0.1 inches (1 to 3 millimeters) across. These stars are green with darker markings.

Geographic range: Tropical brittle stars live all over the world.

Habitat: Tropical brittle stars live among algae and sponges and hide in reef crevices.

Diet: Tropical brittle stars eat small particles from the surface they live on or from the open water.

Behavior and reproduction: Tropical brittle stars use both sexual reproduction and splitting. When these brittle stars split, the body softens, forms a groove, and tears into jagged halves, which grow into new six-armed stars. Tropical brittle stars begin reproducing sexually when they are larger than 0.1 inch (3 millimeters) across. The larvae drift freely and feed on microscopic animals drifting in the water.

Tropical brittle stars and people: Tropical brittle stars have no known importance to people.

Conservation status: Tropical brittle stars are not considered threatened or endangered. ∎