Common Brittle Star

Overview

The Common Brittle Star (Ophiothrix fragilis) is a small, delicate echinoderm widely distributed across the northeastern Atlantic and Mediterranean. Known for its resilience and ability to regenerate lost limbs, this species is frequently found in dense, massive aggregations on the seafloor.

Appearance

This brittle star features a central, pentagonal disc typically measuring up to 2 cm in diameter, from which five long, slender, and highly flexible arms extend. These arms, which can reach five times the disc's diameter, are covered in numerous glassy, serrated spines that give the animal a bristly, untidy appearance. Their coloration is extremely variable, ranging from white, yellow, and orange to red, purple, or grey, often with distinct banding or spotting on the arms.

Distribution & habitat

Ophiothrix fragilis is found from the coasts of Norway and the British Isles south to South Africa. It thrives in various environments, including rocky shores, crevices, and mixed sediments like gravel or pebbles. While often found as solitary individuals hiding under rocks or within sessile organisms, they are well-known for forming expansive, high-density beds in current-swept areas.

Biology & behavior

Primarily nocturnal, these brittle stars often remain hidden during the day and emerge to feed. They are capable of autotomy, a defense mechanism where they intentionally shed an arm if threatened, which they can later regrow. They move across the seafloor using a graceful, snake-like wriggling motion of their arms. As suspension feeders, they extend their arms into the water column to trap plankton and organic particles using sticky tube feet, playing a vital role in transferring nutrients from the water to the benthos.