Phylum Echinodermata: Echinoderms are marine animals and can be found in the depths of the ocean as well as in the intertidal zone. An interesting feature of this phylum is that all animals belonging to Echinodermata are marine. There are no freshwater or terrestrial organisms in this phylum. Water vascular system present in the echinoderms is a unique circulatory system. This accounts for the gaseous exchange, circulation of nutrients, waste elimination as well as locomotion. This system has a central ring canal and radial canals that extend along each arm. Through these structures, water circulates. The madreporite is a structure present on top of the body. This is responsible for regulation of the water in the water vascular system.

• These animals have an endoskeleton of calcareous ossicles [calcium carbonate structures] and, hence, the name Echinodermata (spiny skinned organisms).
• They are exclusively free-living marine animals with organ-system level of organisation.
• They are triploblastic with a coelomic cavity [coelomate animals]. The adult echinoderms are radially symmetrical but larvae are bilaterally symmetrical.
• Water-driven tube system [water vascular system] are used for locomotion, capture and transport of food and respiration.
• They are triploblastic and coelomate animals.
• Digestive system is complete. An excretory system is absent.
• Sexes are separate. Reproduction is sexual. Fertilisation is usually external.
• Development is indirect with free-swimming larva.
• Examples: Star fish, Sea urchin, Sea lily, Sea cucumber, Brittle star.

Classification of Phylum Echinodermata

Asteroidea

• They have a flattened, star-shaped body with five arms.

• They have tube feet with suckers.

• They respire through papulae.

• The body comprises of calcareous plates and movable spines.

• Pedicellaria is present.

• Eg., Asterias, Zoroaster

Ophiuroidea

• The body is flat with pentamerous discs.

• The tube feet are devoid of suckers.

• They respire through Bursae.

• The long arms are demarcated from the central disc.

• Eg., Ophiderma, Amphuria

Echinoidea

• The body is hemispherical.

• The tube feet contains suckers.

• The body does not have arms.

• The body has a compact skeleton and movable spines.

• Eg., Echinus, Cidaris

Holothuroidea

• The body is long and cylindrical.

• The arms, spines, and pedicellariae are absent.

• They respire through the cloacal respiratory tree.

• They possess tube feet with suckers.

• Eg., Cucumaria, Holothuria

Crinoidea

• The body is star-shaped.

• The tube feet have no suckers.

• The arms are bifurcated.

• Spines and pedicellariae are absent.

• Eg., Neometra, Antedon

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By Team Learning Mantras