Ophiomusa

Lore & Background

Ophiomusa belongs to the class Ophiuroidea, commonly known as brittle stars. These echinoderms have a central disc ranging from 6 to 12 mm in diameter, with arms that can exceed four times the disc diameter in length. The arms are composed of calcium carbonate plates and are spiny, aiding in locomotion and feeding. The first dorsal arm plates are trapezoidal, while subsequent ones are triangular and separated from each other. Brittle stars lack a brain and eyes but possess a stomach, sex organs, and a mouth with five jaws located on the oral surface, which faces downward but is held off the sea floor. They can regenerate severed arms and even voluntarily cut off an arm (autotomy), which gives them their common name.

Reader's Guide

Ophiomusa, as part of the brittle star group, holds significance in marine ecosystems due to its widespread distribution across both tropical and polar regions, including high-density populations observed off the North Carolina coast and along the Yucatán Peninsula. Despite their almost cosmopolitan range, little is known about them. Their diet varies by habitat: shallow-water individuals consume plankton and macroalgae, while deep-sea individuals often feed on brittle star fragments. Gut content studies have also revealed macroalgae, diatoms, bivalves, gastropods, cyanobacteria, marine fungi, and unidentified eggs. Reproduction occurs both asexually (through fission of the disc) and sexually, with most species being hermaphrodites. Fertilized eggs develop into plankton-feeding larvae called Ophioplutei, which undergo metamorphosis to develop five arms before settling on the seafloor. Sexual maturity is reached after about two years, and lifespans can reach up to five years. Their ability to autotomize and regenerate arms is a key survival trait.

Did You Know?

• Brittle stars do not have a brain or eyes, but they have a stomach, sex organs, and a mouth with five jaws.
• Ophiuroids can reproduce asexually by splitting their disc in half, a process called fission.
• The larvae of brittle stars are called Ophioplutei and feed on plankton.
• Brittle stars can voluntarily cut off their own arm (autotomy) to escape predators.