Biology · Animal Kingdom · NEET
It depends on the STAGE. The adult echinoderm (like a starfish) is radially symmetrical — its body parts are arranged around a central point, usually in fives. But the larva is bilaterally symmetrical — it can be cut into equal left and right halves in only one plane. NCERT says exactly this: 'The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.' So the safe answer for NEET is: ADULT = radial, LARVA = bilateral.
Scientists believe the ancestors of echinoderms were bilaterally symmetrical, free-moving animals. The larva still shows this old ancestral body plan because it swims freely and needs a front end to move forward, like a worm. When the larva settles and becomes an adult, its body reorganises into radial symmetry, which suits a slow, bottom-living lifestyle. So bilateral symmetry in the larva is like a memory of the echinoderm's evolutionary past. For NEET you just need the fact; the reason is a bonus.
The starfish larva is bilaterally symmetrical. The adult starfish is radially symmetrical (five arms around a centre). NEET 2020 tested this exact match: 'Adult with radial symmetry and larva with bilateral symmetry' was matched to Asterias (starfish). So remember: adult starfish = radial, larva = bilateral.
No. This is the most common trap. Only the ADULT is radial. The LARVA is bilateral. If a question says 'both adults and larvae of Echinodermata are radially symmetrical,' that statement is WRONG. ReNEET 2026 used this exact false statement to trick students.
Only phylum Echinodermata shows this special mix — bilateral larva and radial adult. Coelenterates and ctenophores are radial at all stages. Most other higher animals (annelids, arthropods, chordates) are bilateral at all stages. So the 'bilateral larva → radial adult' switch is a signature clue that points to Echinodermata.
Yes. Even though adults look radial, echinoderms are triploblastic (three germ layers) and coelomate (true body cavity). Their radial symmetry is secondary, gained during development, not from a primitive diploblastic body like coelenterates. NEET 2021 confirmed 'Echinoderms are triploblastic and coelomate animals' as a correct statement.
Statement I: When any plane passing through the central axis of the body divides the organism into two identical halves, it is called radial symmetry. Statement II: In phylum Echinodermata, both adults and larvae are radially symmetrical. Choose the most appropriate answer:
Select the incorrect statements from the following: A. Digestive system in Platyhelminthes is incomplete. B. Bilateral symmetry is a characteristic feature of adult Echinoderms. C. Pseudocoelom is possessed by Aschelminthes. D. Notochord is persistent throughout life in the class Chondrichthyes. E. Members of class Reptilia maintain a constant body temperature.
Match the following columns and select the correct option. Column-I: (a) Gregarious, polyphagous pest (b) Adult with radial symmetry and larva with bilateral symmetry (c) Book lungs (d) Bioluminescence. Column-II: (i) Asterias (ii) Scorpion (iii) Ctenoplana (iv) Locusta
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Adult echinoderms have RADIAL symmetry. This is the standard NEET answer. Their larvae have bilateral symmetry.
Asterias (starfish) is the classic example. The adult starfish is radially symmetrical, but its larva is bilaterally symmetrical. Ophiura (brittle star) and other echinoderms follow the same pattern.
No. In coelenterates radial symmetry is primary and they are diploblastic. In echinoderms the radial symmetry is secondary — it develops from a bilateral larva, and the animals are triploblastic and coelomate. This difference is a favourite NEET point.
Hemichordates are bilaterally symmetrical as adults, unlike adult echinoderms which are radial. NEET 2023 asked which phylum does NOT show radial symmetry in adults — the answer was Hemichordata.
Because it is a small exception that is easy to flip in a statement. Adult = radial, larva = bilateral is a one-line NCERT fact that appears in statement-type, match-type, and assertion-reason questions almost every year, as seen in NEET 2020, 2026 and ReNEET 2026.
