Q.Distinguish the symmetry seen in the larva and the adult of an echinoderm.
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Phylum Echinodermata – From Intuition to Precision
Imagine walking along a rocky seashore at low tide. You spot a starfish clinging to a rock, its five arms spread out like a living star. Nearby, a sea urchin bristles with spines, and a soft, cucumber-shaped creature lies half-buried in the sand. These animals look nothing like fish or crabs. They belong to a group called Echinoderms — a name that literally means "spiny-skinned" (from Greek echinos = hedgehog/spiny, derma = skin).
What makes them truly strange is that as adults, they are radially symmetrical — usually in multiples of five — like a living wheel. But here's the twist: their larvae are bilaterally symmetrical, like most other animals. This means an echinoderm starts life looking like a tiny, two-sided creature, then reorganises its entire body plan into a five-part adult. That is a radical transformation.
The Precise Statement
Phylum Echinodermata includes exclusively marine, triploblastic, coelomate animals with an endoskeleton of calcareous ossicles, a unique water vascular system that powers tube feet for locomotion and feeding, and pentaradial symmetry in adults (bilateral larvae). Example: Asterias (starfish), sea urchin, sea cucumber.
The Key Features, One by One
1. Endoskeleton of calcareous ossicles.
The skeleton is not on the outside like a crab's shell. It is internal — made of tiny, calcium-carbonate plates (ossicles) embedded in the skin. In a starfish, these plates are loosely connected, giving it flexibility. In a sea urchin, they fuse into a rigid, globular test (the hard shell you might find on a beach). Spines project from these ossicles, giving the phylum its name.
2. Water vascular system.
This is the echinoderm's superpower. It is a network of fluid-filled canals that open to the outside through a sieve-like plate (the madreporite). By contracting muscles around the canals, the animal forces water into hundreds of tiny, hollow tubes called tube feet that stick out from the underside. Each tube foot ends in a suction cup. The starfish uses these to grip rocks, pry open clam shells, and even walk — slowly, but deliberately.
Think of the water vascular system as a hydraulic system. The animal squeezes water into the tube feet to extend them, then releases pressure to retract them. It is like a living, water-powered hand.
3. Radial symmetry in adults.
Most echinoderms have five arms or five-part body organisation (pentaradial symmetry). A starfish has five arms radiating from a central disc. A sea urchin has five rows of tube feet running from mouth to anus. But this symmetry is secondary — their larvae are bilateral, and some echinoderms (like sea cucumbers) have re-evolved a bilateral shape while keeping internal five-part organisation.
4. Exclusively marine.
No echinoderm lives in freshwater or on land. They are found from tide pools to the deep sea.
5. Triploblastic and coelomate.
They have three germ layers (ectoderm, mesoderm, endoderm) and a true coelom (body cavity lined with mesoderm). The coelom is spacious and forms the water vascular system and other internal spaces.
Examples You Should Know
| Common Name | Example | Key Feature |
|---|---|---|
| Starfish / Sea star | Asterias | Five arms, tube feet with suckers, can regenerate lost arms |
| Sea urchin | Echinus | Globular body, long spines, five-part test |
[!TLDR] Echinoderm larvae are bilaterally symmetrical, while the adults are (typically penta-)radially symmetrical. …
[!ANSWER] Echinoderms show a striking change in body symmetry between the larval and adult stages.
The free-swimming, ciliated larva of a typical echinoderm is bilaterally symmetrical — it has a distinct left and right side that mirror each other, much like the larvae or adults of most other animal groups. However, as this larva undergoes metamorphosis into the sessile or slow-moving adult form, its body reorganises into a radially symmetrical plan, most commonly a pentaradial (five-part) arrangement, as clearly seen in the five arms of a typical starfish or the five-part structure underlying a sea urchin's test. …
- Assuming echinoderms are radially symmetrical throughout their entire life cycle, including as larvae. …
- CBSE 2026Set ANNUAL1 markQ.Answer in one word/sentence: Water vascular system is a characteristic of which phylum?
›Reveal solutionSolution
The water vascular system — a distinctive network of water-filled canals ending in tube feet — is unique to and characteristic of Phylum Echinodermata.
Echinoderms (starfish, brittle stars, sea urchins, sea cucumbers, feather stars) possess a unique hydraulic system called the water vascular system, derived from the coelom, consisting of a ring canal and radial canals that extend into numerous tube feet (podia). This system, operated through changes in hydraulic pressure, is used for locomotion, capturing a …
- CBSE 2026Set ANNUAL1 markMCQQ.In which phylum is the water vascular system found ?(a) Mollusca(b) Echinodermata(c) Arthropoda(d) Anelida
›Reveal solutionSolution
The water vascular system is unique to phylum Echinodermata, so the answer is (B).
The water vascular system is a network of fluid-filled canals connected to tube feet (podia). It is used for locomotion, capture and transport of food, and respiration. This system is a defining, unique feature of phylum Echinodermata (starfish, sea ur …
- CBSE 2025Set zoology-hz1 markMCQQ.The mouth is located on ventral side of the body in:(a) Mollusca(b) Porifera(c) Echinodermata(d) All the above
›Reveal solutionSolution
In Echinodermata, the mouth lies on the ventral (oral) surface and the anus on the dorsal (aboral) surface of the body.
Echinoderms (e.g. Asterias/starfish, Echinus/sea urchin, Antedon) are exclusively marine, triploblastic, coelomate animals with an endoskeleton of calcareous ossicles and a unique water vascular system used for locomotion, capture of food and respiration. The adult body shows pentamerous radial symmetry (though the larva is bilaterally symmetrical), organised around two distinct surfaces:
- The oral (ventral) surface, which bears the mouth.
- The aboral (dorsal) surface, which bears the anus. …
- CBSE 2024Set ANN1 markQ.Water vascular system is present in __________.
›Reveal solutionSolution
The water vascular system is a defining feature of phylum Echinodermata, to which starfish belongs.
Among the given options — Leech (Annelida), Nereis (Annelida), Prawn (Arthropoda), Starfish (Echinodermata) — only echinoderms possess a unique hydraulic system called the water vascular system, used for locomotion, capture of food, and respiration through structures called tube feet (podia). Leech and Ne …
- CBSE 2023Set ANNUAL1 markMCQQ.Water vascular system is present in animals belonging to phylum(a) Arthropoda(b) Annelida(c) Mollusca(d) Echinodermata
›Reveal solutionSolution
The water vascular system, made of canals and tube feet used for locomotion and feeding, is a hallmark feature unique to phylum Echinodermata.
Each animal phylum in the NCERT classification has a small set of diagnostic features that distinguish it from the others, and the water vascular system is one of the most distinctive.
What the water vascular system is: it is a network of water-filled canals (the ring canal and radial canals) derived from the coelom, connecting to numerous external tube feet (podia). Water enters through a sieve-like plate called the madreporite, and by hydraulic pressure changes, the tube feet extend and contract. This system is used for locomotion, capturing and moving food towards the mouth, and respiration.
Why the other options are wrong:
- Arthropoda (e.g., insects, crustaceans) is characterised by a chitinous exoskeleton and jointed appendages, not a water vascular system. …
- CBSE 2022Set TERM11 markMCQQ.The role of tube feet in water vascular system is(a) Locomotion(b) Ingestion(c) Respiration(d) All of these
›Reveal solutionSolution
Echinoderm tube feet are multi-purpose organs: they help the animal move, feed, and breathe.
Echinoderms (e.g., starfish, sea urchins) possess a unique water-driven tube feet system called the water vascular system, radiating from a central ring canal. The tube feet (podia) project out through the body wall and are operated by hydraulic pressure. NCERT explicitly notes that these tube feet are used for locomotion (the animal 'walks' on its many tube feet), for capture and movement of food (grasping prey, passing food particles towards the mouth), and for resp …
- CBSE 2020Set ANNUAL1 markMCQQ.Water vascular system is present in animals belonging to the Phylum(a) Porifera(b) Arthropoda(c) Echinodermata(d) Mollusca
›Reveal solutionSolution
The water vascular system, a network of water-filled canals ending in tube feet, is a defining feature unique to phylum Echinodermata.
Echinodermata (spiny-skinned animals such as starfish, sea urchins, brittle stars, and sea cucumbers) are exclusively marine. Their most distinctive feature is the water vascular system — a network of canals (ring canal, radial canals) derived from the coelom, ending externally in tube feet (podia).
- The tube feet help in locomotion, capturing food, and respiration. …
- CBSE 2020Set ANNUAL1 markMCQQ.Presence of water vascular system is found in:(a) Phylum Annelida(b) Phylum Arthropoda(c) Phylum Mollusca(d) Echinodermata
›Reveal solutionSolution
The water vascular system is exclusive to Phylum Echinodermata (starfish, sea urchins, brittle stars).
The water vascular system is a network of water-filled canals (ring canal, radial canals, lateral canals) connected to numerous external tube feet (podia), which work hydraulically for locomotion, capturing food and respiration.
- (a) Phylum Annelida — segmented worms use chaetae/parapodia for locomotion, not a water vascular system. …
- CBSE 2019Set ANNUAL1 markQ.Fill in the blank: Starfish has been placed in the phylum ______.
›Reveal solutionSolution
Starfish (sea star) belongs to phylum Echinodermata, characterised by a spiny calcareous endoskeleton and water-vascular system.
Echinodermata (from Greek 'echinos' = spiny, 'derma' = skin) is an exclusively marine phylum that includes starfish, sea urchins, brittle stars, sea cucumbers, and feather stars. Members show a distinctive spiny calcareous endoskeleton just beneath the skin, and a unique water-vascular system of canals ending in tube feet used for locomotion, food capture, and respiration. Adults typical …
- CBSE 2018Set ANNUAL1 markQ.Match the following. Column A item: 'Star fish'. Choose its correct match from Column B:(1) Casein(2) Water vascular system(3) Fixation of CO2(4) Bentham and Hooker(5) Cockroach
›Reveal solutionSolution
'Star fish' matches 'Water vascular system' — echinoderms like the starfish possess a distinctive water-driven hydraulic system used mainly for locomotion.
The water vascular system is a network of water-filled canals unique to phylum Echinodermata (starfish, sea urchins, brittle stars, etc.). It originates from a sieve-like madreporite on the body surface, connects through a stone canal to a ring canal, and then to radial canals running along each arm, from which numerous tube feet (podia) project. By hydraulic pressure changes, these tube feet extend and retract, allowing the starfish to move, capture food …
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