Each ophiuroid arm is a chain of vertebral ossicles joined by connective tissue whose stiffness the animal can alter under nervous control. When gripped, the brittle star can soften the tissue at a chosen joint and let the distal portion detach, a process called autotomy. The break is clean rather than ragged, and it happens fast enough to leave the predator holding only the shed segment.
Regeneration then proceeds from the stump. Recovery is slow compared with the loss, typically taking weeks to months for substantial arm length, and the regrown tip is often visibly paler and thinner than the original for some time.
The common error is to read the name as a description of fragility. Brittle stars are not weak; the breakage is a controlled defence. What remains an active area of study is how mutable collagenous tissue changes stiffness so quickly, since the mechanism involves nerve-triggered chemical modification of the connective tissue rather than muscle action.