Question
Give salient features of phylum Echinodermata.
✓
Answer
Salient features of phylum Echinodermata (Echinus – spines, derma – skin)
- Habitat: These are exclusively marine.
- Forms: Members of this phylum are solitary, sedentary or free-living and gregarious, benthic.
- Body symmetry: These animals are radially symmetrical with pentamerous symmetry.
- Shape: Members of Echinodermata are spherical, elongated or star-shaped.
- Body: The endoskeleton is made up of calcareous ossicles. Spines are formed on the body. Hence, they are known as echinoderms. The body has two sides oral and aboral and lacks definite divisions. Mouth is ventrally present on oral surface and anus on aboral surface.
- Water vascular system: Presence of water vascular system is the peculiar character of echinoderms. The madrepOrite is the opening of water vascular system through which water enters. Water vascular system is useful in locomotion, food capturing, respiration.
- Digestion: Digestive system is complete.
- Respiration: Peristomial gills, papillae, respiratory tree, etc. are used for respiration.
- Circulatory and excretory systems: Absent in echinoderms.
- Nervous system: Nervous system is simple with a nerve ring around the mouth and radial nerves in arms.
- Reproduction and development: Sexes are separate (sometimes bisexual). Fertilization is external.
- Development is indirect, i.e. through larval stages. They show high power of regeneration.
e.g. Sea lily (Antedon), Sea star (Asterias), Sea cucumber (Cucumaria), Brittle star (Ophiothrix), Sea urchin (Echinus).
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