Biology · Ch 4 — Animal Kingdom
Phylum – Echinodermata
Phylum – Echinodermata
The animals of this phylum carry an internal skeleton (endoskeleton) built from calcium-containing plates called ossicles, and their spiny bodies give the phylum its name, which means spiny bodied. Every member is marine, and they show an organ-system level of organisation.
Symmetry, layers and cavity
- The adults are radially symmetrical, with parts arranged around a central axis, but the larvae are bilaterally symmetrical, so symmetry changes during the life cycle.
- They are triploblastic.
- They are coelomate, possessing a true body cavity.
Digestive system
The digestive system is complete, with the mouth on the lower or ventral surface and the anus on the upper or dorsal surface.
The water vascular system
The most distinctive feature of echinoderms is a water vascular system. This unique system of fluid-filled canals and tube feet helps in locomotion, in capturing and moving food, and in respiration.
Excretion and reproduction
- A separate excretory system is absent.
- The sexes are separate.
- Reproduction is sexual.
- Fertilisation is usually external. …
Drawn by us to help you understand the concept clearly, and verified to make sure it's accurate. For exams, practice from your NCERT textbook's own diagram.
These are echinoderms, meaning spiny-skinned animals, of phylum Echinodermata. They are all marine and have an internal skeleton of calcareous plates, often bearing spines. Their most special feature is the water-vascular system, a network of water-filled canals that operate tiny tube feet used for slow movement, capturing food and breathing. Interestingly, their larvae are bilaterally symmetrical but the adults show radial symmetry, usually built on a five-part pattern. Asterias is the starfish, Ophiura is the brittle star with slender arms, and Cucumaria is the soft, …