In a specimen-based viva, the examiner describes this case: a specimen has slender flexible arms sharply set off from the central disc. Choose the concept that fits it best.

Brittle stars belong to Ophiuroidea. Their long flexible arms are clearly distinct from the central disc and are used for movement. This MCQ belongs to the Ophiuroidea topic in Animal Diversity-I and is written to test concept understanding rather than memorized wording.