The members of Phylum Echinodermata are exclusively marine animals, till now these are not found as terrestrial or freshwater. About seven thousand living species are included in this phylum. The adults are recognizable by their radial symmetry. The Phylum includes starfish, sea urchins, sand dollars, and sea cucumbers, as well as the sea lilies or “stone lilies. The Echinoderms are the largest phylum that has no freshwater or terrestrial members.
Characteristics features of Echinoderms:
- these are spiny bodies and having an endoskeleton of calcareous ossicles.
- These possess a star-like appearance and may be of elongated or spherical shape.
- Level of organization: Organ-system
- Symmetry: The adult shows a radially symmetrical body while the larvae possessed a bilaterally symmetrical body.
- Germinal layers: they are triploblastic
- Body cavity or coelom: These are Coelomate animals.
- They possess an unsegmented body, the head is not distinct.
- They consisting of a complete digestive system.
- The mouth is on the lower i.e. ventral side, and the anus is situated on the upper- dorsal side.
- absence of the excretory system
- The most distinctive feature: water vascular system.
- The phylum shows a unique water vascular system. The water vascular is a network of fluid-filled canals derived from the coelom (body cavity) system that helps in the gas exchange, locomotion, capture, and transportation of food, sensory reception, and respiration.
- This system varies between different classes of echinoderm but typically opens to the exterior through a sieve-like madreporite on the aboral (upper) surface of the animal.
- Sense organs are poorly developed and simple nervous systems.
- Reproduction: Sexes are separate, sexual reproduction.
- Generally external fertilization.
- Indirect development with free-swimming larva.
- They consisting the power of regeneration
- Examples of Echinoderms: Asterias (starfish), Echinus (sea urchin), Antedon (sea lily), Cucumaria (sea cucumber), and Ophiura (Brittle star).
Scientific Classification of Echinoderms
Five classes of echinoderms
- Asteroidea– (Sea-stars) Most of the echinoderms belong to this class.
- They possess a star-shaped, flattened body having five arms.
- In these members the pedicellaria is present.
- They possess tube feet with suckers, which helps in gripping the surface and to capture prey.
- Respiration is through papulae.
- Examples; Asterias and Zoroaster.
- Ophiuroidea– (Brittle star)
- These possess a flat body with a pentamerous disk.
- They are generally scavenger and detritivores
- They consisting of tube feet devoid of suckers.
- They possess long thin arms that are demarcated from the central disk.
- Example: Ophiderma, Amphuria
- Echinoidea- (sea urchins and sand dollars)
- They are consisting of hemispherical body
- The members consist of Tube feet with suckers.
- No arms are found in these animals.
- A compact skeleton and spines are found.
- example: echinus, Cidaris.
- Holothuroidea– (Sea-cucumbers)
- They possess an endoskeleton just below the skin.
- They consisting of tube feet with the sucker.
- The animals having a long and cylindrical body.
- respiration is through the cloacal respiratory tree.
- examples: Cucumaria, Holothuria.
- Crinoidea – (sea lilies or feather star)
- The animals are of star-shaped bodies.
- The tube feet without suckers.
- They are consisting of bifurcated arms.
- Examples: Neometra, Antedon.
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