Ophiocoma echinata
A large brittle star with coordinated locomotion and no brain.
Ophiocoma echinata, called the spiny ophiocoma, is a brittle star and the type species for its genus, Ophiocoma. It lives in the tropical west Atlantic, the Caribbean Sea, and the Gulf of Mexico.
This is a large brittle star, with arms that can span up to 25 cm. The arms are slender, taper toward the tips, and are thickly covered in short spines. They are clearly set off from the central disc. The animal is dark in color with pale or cream markings, but red is never present on the arms.
The species is common across the Caribbean down to about 30 meters deep. It hides under rocks, in cracks and crevices, beneath coral heads, and inside sponges. It also lives in seagrass meadows, on reefs, and on reef flats.
To feed, O. echinata holds some arms upright in the current, catching particles on its spines and moving them along channels to its mouth. The stomach, located entirely inside the disc, stores food. It uses its arms to burrow into sand and anchor itself in crevices. For movement, it lifts its disc off the bottom while its tube feet grip the surface. Even without a brain—only a simple ring-shaped nervous system—it moves in a coordinated way: one arm leads while the others work together to push it forward. To change direction, it does not turn; instead, a different arm takes the lead. This shows that a radially symmetrical animal can perform fully coordinated, bilaterally symmetrical locomotion.
When a predator attacks, the brittle star may shed one or more arms. In a back-reef area of the Florida Keys, up to 47% of individuals had missing or damaged arms. It took about two years for those missing three arms to fully regrow them. Losing a limb instead of its life benefits the brittle star: though it must use energy for repair and regrowth, it can still breed later, and the lost arm becomes a renewable resource for the reef’s productivity.
Quick Facts
- Genus
- Ophiocoma
- Species
- echinata
Facts from the source article.
Lore & Background
Ophiocoma echinata is a large brittle star with slender, tapering arms densely clad with short spines, clearly demarcated from the disc. Its colour is dark with pale or cream-coloured markings, and the arms never have any red markings. It is native to the tropical west Atlantic Ocean, the Caribbean Sea, and the Gulf of Mexico, common throughout the Caribbean at depths down to about 30 metres. It inhabits seagrass meadows, reefs, and reef flats, hiding under rocks, in cracks and crevices, under coral heads, and inside sponges.
Reader's Guide
Ophiocoma echinata is significant as the type species of the genus Ophiocoma, providing a reference for the group. Its ability to coordinate locomotion without a brain, using a simple ring-shaped nervous system, illustrates how radially symmetrical animals can achieve bilaterally symmetrical movement. This challenges assumptions about the necessity of a centralized brain for complex motor control. The species also demonstrates a notable regenerative capacity: individuals missing three arms can fully regenerate them over about two years, and up to 47% of individuals in a Florida Keys back-reef habitat showed arm damage. Autotomy (shedding arms) is a survival strategy that allows the brittle star to escape predators, diverting energy to repair and regrowth while still enabling future breeding. The lost arm contributes a renewable resource to reef productivity. Its feeding method—filtering particles from currents using arm spines—and its habitat preferences (seagrass meadows, reefs, crevices, sponges) further highlight its ecological role in Caribbean and Gulf of Mexico waters.
Did You Know?
- Ophiocoma echinata is the type species of the genus Ophiocoma.
- It can reach a maximum armspan of 25 cm (10 in).
- Despite having no brain, it coordinates locomotion with one arm leading and the others acting in synchrony.
More in Sea Cucumbers and Brittle Stars, Part 3 1-24
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