SEA DAISIES: Concentricycloidea

PHYSICAL CHARACTERISTICS

Sea daisies are small, circular animals related to sea stars. There are only two species. Sea daisies have no arms, but the circle is rimmed with flat spines that look like daisy petals. The upper surface of the animal is delicately plated. The bottom surface has a mouth frame that leads to a shallow stomach and has a single ring of tube feet. Sea daisies are 0.4 to 0.6 inches (10 to 14 millimeters) across. They are see-through but not clear, like fogged-up glass. These animals have a water circulation system arranged in rings. The sexes are separate.

GEOGRAPHIC RANGE

Sea daisies live near New Zealand and the Bahamas.

HABITAT

Sea daisies live on sunken wood in water deeper than 3,280 feet (1,000 meters).

DIET

Sea daisies eat bacteria, dissolved nutrients on sunken wood, waste, and possibly microscopic mollusks. Mollusks (MAH-lusks) are animals with a soft, unsegmented body that may or may not have a shell.

BEHAVIOR AND REPRODUCTION

To move to new habitats, sea daisies use pulsing actions of their stomach or drift like parachutes. Sea daisies have separate sexes and mate rather than releasing eggs and sperm into the water. In one species the fertilized (FUR-teh-lyzed) eggs, those that have joined with sperm, develop inside a female, who gives birth to live young. In the other species the fertilized eggs are laid, and the young develop outside the female's body. The developing young are cone-shaped or flat.

SEA DAISIES AND PEOPLE

Sea daisies have no known importance to people.

CONSERVATION STATUS

Sea daisies are not considered threatened or endangered.

MEDUSIFORM SEA DAISY (Xyloplax medusiformis): SPECIES ACCOUNT

Physical characteristics: Medusiform (mih-DOO-seh-form) sea daisies are circular and slightly inflated. The body is 0.4 inches (9 millimeters) across, including the spines around the rim. The spines are all one length: 0.002 to 0.003 inches (40 to 75 micrometers). The mouth frame has ten to thirty bones. Medusiform sea daisies do not have a stomach. Instead there is a thin, flexible sheet on the bottom surface of the daisy that is supported by the mouth frame.

Geographic range: Medusiform sea daisies live on the east and west coasts of New Zealand.

Habitat: Medusiform sea daisies live on sunken wood in deep water.

Diet: Medusiform sea daisies absorb dissolved nutrients from decomposing wood.

Behavior and reproduction: Scientists do not know how medusiform sea daisies behave. They have separate sexes and mate. The young develop inside the females.

Medusiform sea daisies and people: Medusiform sea daisies have no known importance to people.

Conservation status: Medusiform sea daisies are not considered threatened or endangered. ∎

FOR MORE INFORMATION

Books:

Brusca, Richard C., Gary J. Brusca, and Nancy Haver. Invertebrates. 2nd ed. Sunderland, MA: Sinauer, 2002.

Periodicals:

Voight, Janet R. "How to Study Animals in Habitiats You've Never Seen." In the Field (spring 2005): 16–17.

Web sites:

"The Echinoderm Phylum." University of Washington School of Aquatic and Fishery Sciences. http://www.fish.washington.edu/classes/fish310/PDF/echino.pdf (accessed on March 9, 2005).