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 sea lilies or “stone lilies. The Echinoderms are the largest phylum that has no freshwater or terrestrial members.
Characteristics features of Echinoderms
Phylum-Echinodermata consists of the following characteristic features:
- These are spiny bodies and have 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 consist 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: is the 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: are Asterias (starfish), Echinus (sea urchin), Antedon (sea lily), Cucumaria (sea cucumber), and Ophiura (Brittle star).
Scientific Classification of Phylum-Echinodermata:
Five classes of echinoderms
Asteroidea– (Sea-stars) Most of the echinoderms belong to this class.
The characteristic features of class Asteroidea:
- They possess a star-shaped, flattened body having five arms.
- In these members the pedicellaria is present.
- They possess tube feet with suckers, which help in gripping the surface and capturing prey.
- Respiration is through papulae.
- Examples; Asterias and Zoroaster.
Ophiuroidea– (Brittle star)
Class Ophiuroidea shows the following features:
- These possess a flat body with a pentamerous disk.
- They are generally scavengers and detritivores
- They consist 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)
Some features of Echinoidea are as follows:
- 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.
Class Holothuroides shows the following features:
- They possess an endoskeleton just below the skin.
- They consist of tube feet with a sucker.
- The animals have long and cylindrical bodies.
- respiration is through the cloacal respiratory tree.
- examples: Cucumaria, Holothuria.
Crinoidea – (sea lilies or feather stars)
Class Crinoidea shows the following features:
- 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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