Greek words Ekina-spines & derma-skin
They have body covered with spiny skin.
Habitat:
They are exclusively marine.
Germ layers:
They are triploblastic containing 3 germ layers.
Symmetry:
Adults are radially symmetrical and larval forms are bilaterally symmetrical.
Body Grade:
They have organ-system grade of body organization.
Coelom:
They are coelomatic. Coelom is surrounded by ciliated peritoneum.
Body division:
The body is unsegmented and variously shaped like globular, star-like, spherical, elongated, flattened or flower-like . Head is absent.
Cephalisation:
Head is absent.
Nutrition:
They exhibit holozoic nutrition.
Alimentary Canal:
Alimentary canal is straight and well-developed.
Digestion:
Digestion is extra-cellular inside the alimentary canal.
Respiration:
Respiration occurs by gills (branches) or papullaprotauding from the dermis, the tube feet and cloacal aperture.
Circulatory System:
Blood vascular system is open type with fine radiating vessels.
Excretion:
The excretory organs are absent. Water vascular system helps in excretion.
Nervous system:
There is lack of centralized nervous system.
SUPERCLASS:PISCES:-
- Body is streamlines, covered by smooth slippery scale for aquatic adaptation.
- Heart is two chambered.
- They are poikilothermic.
- Respiration occurs by gills and gills are protected by operculum.
- They bear ten pairs if cranial nerves.
- Lateral line is present in the lateral size of body that helps in detecting water pressure.
- Swim bladder is present for hydrostatic function.
- Locomotion occurs by fins.
- Body is divided into head, trunk and tail. Tail is powerful propulsive organ.
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