Brittle Star (Ophiothrix spiculata)
Contributed by TPERP Victor Knarreborg
Where to find them: This species is most abundant in the middle and low intertidal pools. Subtidally, it can live to depths of more than 200 feet. The geographic range is from San Mateo County in northern California to Peru.
What do they eat: The Spiny brittle star is not a bottom scavenger, but a suspension feeder. It raises its arms upward and traps suspended plankton and detritus with mucus secretions on the arms and spines.
Size and Color: A brittle star has five unbranched arms, set off from a central disc. The arms appear to be jointed because of four longitudinal rows of shields. There are two rows of lateral shields with two to 15 spines arranged in rows. Spines vary in shape and size depending on the species. A variety of colors are seen among brittle stars and they are often mottled or banded, but most at Cabrillo are greenish brown with orange bands around the arms. The central disc of most species ranges from 0.39–1.2 inches in diameter.
Reproduction: The gonads are located in the disk, and open into pouches in between the arms, called genital bursae. Fertilization is external in most species, with the gametes being shed into the surrounding water through the bursal sacs. An exception is the Ophiocanopidae, in which the gonads do not open into bursae and are instead paired in a chain along the basal arm joints.
Brittle stars generally sexually mature in two years, become full grown in three to four years, and live up to five years. Euryalina, such as Gorgonocephalus, may well live much longer.
Interesting facts: Brittle stars are the most mobile echinoderms. Flexible arms are used for crawling or clinging. The lateral arm spines provide traction.
Brittle stars occur in incredible numbers on the sandy seafloor. In kelp forests near La Jolla in southern California, millions of them may carpet the seafloor in layers up to an inch thick.
Brittle stars live in an incredible range of water depths—from the shoreline down to 6,755 feet.
Over 60 species of brittle stars are known to be bioluminescent. Most of these produce light in the green wavelengths, although a few blue-emitting species have also been discovered. Both shallow water and deep-sea species of brittle stars are known to produce light. Presumably, this light is used to deter predators.
There are over 2,000 species of brittle stars living today. More than 1200 of these species are found in deep waters, greater than 200 meters deep.
The name is derived from their habit of breaking off arms as a means of defense. New arms are easily regenerated. Each arm contains a series of jointed, bone-like internal calcite plates, or ossicles, which determine the freedom of arm movements. The body and arms of brittle stars are also protected by calcite plates, which in some species consist of arrays of microlenses that focus light onto a nerve bundle, acting like a compound eye. Brittle stars can move quickly and in any direction.
Classification
Phylum: Echinodermata1
Class: Ophiuroidea1
Order: • Oegophiurida• Phrynophiurida• Ophiurida
Family: Ophiothricidae
Scientific Name: Ophiothrix spiculata
Common Name(s): brittle star. They are also known as serpent stars.
REFERENCES
- SeaWorld Parks & Entertainment. ©1994-2013 SeaWorld Inc. http://www.seaworld.org/animal-info/animal- bytes/animalia/eumetazoa/coelomates/deuterostomes/echinodermata/brittle-stars.pdf
- Monterey Bay Aquarium. © 1999-2013, Monterey Bay Aquarium Foundation
- ITIS, the Integrated Taxonomic Information System!. We are a partnership of U.S., Canadian, and Mexican agencies (ITIS-North America); other organizations; and taxonomic specialists. ITIS is also a partner of Species 2000 and the Global Biodiversity Information Facility (GBIF). The ITIS and Species 2000 Catalogue of Life (CoL) partnership is proud to provide the taxonomic backbone to the Encyclopedia of Life (EOL).
http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=157794
Last revised 23-Jan-20
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