Biology · Animal Kingdom · NEET
It is both, but at different life stages. The ADULT echinoderm is radially symmetrical (body parts arranged around a central axis, like a starfish's arms). The LARVA is bilaterally symmetrical (has a left and right half). NEET loves to test this exact line. Remember: adult = radial, larva = bilateral. If a question says 'adult echinoderms are bilaterally symmetrical', it is WRONG.
The bilateral larva shows that echinoderms evolved from bilateral ancestors and are still closely related to chordates. The radial adult symmetry developed later as an adaptation to a slow, bottom-living marine life. For NEET, you mainly need the fact: larva bilateral, adult radial. This is one of the most repeated traps.
Echinoderms are true COELOMATES. They are also triploblastic (three germ layers) and have organ-system level of organisation. NEET 2021 directly asked this: 'Echinoderms are triploblastic and coelomate animals' is a CORRECT statement. Do not confuse them with Aschelminthes (pseudocoelomate) or Platyhelminthes (acoelomate).
It is a network of water-filled canals unique to echinoderms. NCERT says it helps in three things: (1) locomotion, (2) capture and transport of food, and (3) respiration. It does NOT do excretion or digestion. NEET 2025 tested this exactly: the correct functions are Respiration + Locomotion and Capture + transport of food.
No. NCERT clearly states 'an excretory system is absent' in echinoderms. This is a favourite one-line trap. Also note: digestive system is COMPLETE (mouth on the lower/ventral side, anus on the upper/dorsal side), sexes are separate, fertilisation is usually external, and development is indirect with a free-swimming larva.
No. Starfish (Asterias) is an ECHINODERM. Jellyfish and sea anemone (Physalia, Aurelia) are COELENTERATES (Cnidaria). Both look radial, so students mix them up. Trick: echinoderms have a spiny calcareous skeleton and a water vascular system; coelenterates have cnidoblasts (stinging cells) and a polyp/medusa body.
Yes. Echinoderm development is indirect, so the free-swimming bilateral larva metamorphoses into the radial adult. NEET 2018 asked which animal does NOT undergo metamorphosis - the answer was Earthworm (direct development), while Starfish, Moth, and Tunicate all DO metamorphose.
Role of the water vascular system in Echinoderms is: A. Respiration and Locomotion, B. Excretion and Locomotion, C. Capture and transport of food, D. Digestion and Respiration, E. Digestion and Excretion. Choose the correct answer:
Read the statements: (a) Metagenesis is observed in Helminths. (b) Echinoderms are triploblastic and coelomate animals. (c) Round worms have organ-system level of body organization. (d) Comb plates present in ctenophores help in digestion. (e) Water vascular system is characteristic of Echinoderms. Choose the correct answer.
Which of the following animals does not undergo metamorphosis?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It means 'spiny bodied'. 'Echino' means spiny and 'derma' means skin. They get the name from an endoskeleton made of calcareous ossicles (hard plates) just under the skin.
All echinoderms are MARINE (sea water only). None are found in fresh water or on land. This is an easy one-mark point for NEET.
Asterias (star fish), Echinus (sea urchin), Antedon (sea lily), Cucumaria (sea cucumber) and Ophiura (brittle star). Learn these names - NEET often uses them in match-the-column questions.
It is COMPLETE. The mouth is on the lower (ventral) side and the anus is on the upper (dorsal) side. But there is NO excretory system.
Sexes are separate (dioecious). Reproduction is sexual, fertilisation is usually external, and development is indirect with a free-swimming larva that later metamorphoses into the radial adult.
