Phylum Echinodermata
FOR VIDEO https://youtu.be/Dzagw8XH05o
(Echinos-spines; derm-skin)
They are spiny skinned or spiny bodied animals.
The term echinodermata was introduced by J.Klein.
Important characteristic features:
• They are exclusively marine animals.
• The body is covered by large number of spines which are generally immovable and protective in function, but in some, the spines are movable and help in locomotion. Few spines also get modified to form organs of defence known as pedicellaria. Eg: Sea urchin, Star fish, etc.
• They possess an organ system level of body organisation. They are triploblastic animals.
• They are unsegmented and pentamerous, radially symmetrical in the adult, but the larval forms are bilaterally symmetrical.
• They possess an endoskeleton in the form of calcareous plates called ossicles embedded in the skin.
• They are true coelomates but a major part of the coelom has undergone a modification to form the water-vascular system which helps in locomotion, capture and transport of food, and respiration.
• Water vascular system or ambulacral system in which sea water enters through a porous plate called madreporite.
• Tube feet: The water vascular system consists of radiating canals and tube like appendages filled with water. These appendages are called tube feet (podia). Their main function is locomotion and capture of food.
• Digestive system: Complete with mouth on the ventral (lower) side and anus on the dorsal (upper side).
• Respiration: It takes place by skin gills which are protruded from the coelom over the skin.
• Circulatory system: It is reduced.
• Excretory system: It is absent. Nitrogenous wastes diffuse out through the gills.
• Nervous system: It is in the form of a central nerve ring with radial nerves extending to each arm.
• Reproduction: Sexes separate. Fertilisation external. Development is indirect through a free swimming larva.
• Echinoderms have a great power of automy and regeneration.
• The common echinoderms are Asterias (star fish or sea star), Echinus (sea urchin), Echinocardium (heart urchin), Antedon (feather star or sea silly), Cucumaria (sea cucumber), Ophiura (brittle star).
Classification of Phylum Echinodermata
Class I: Asteroidean (star shaped with 5arms. Eg: star fish)
Class II: Ophiuroidea (arms slender and flexible. Eg : brittle fish)
Class III: Echinoidea (no arms, globular body with long spines. Eg: sea urchin)
Class IV: Holothuroidea (no arms, long body with long spines. Eg: sea cucumber)
Class V: Crinoidea (arms slender and forked with branches. Eg: sea lily)
0 Comments