Echinodermata:
- Echinoderms exhibit an endoskeleton of calcareous ossicles.
- Digestive system is complete with mouth on the lower side i.e. ventral side and anus on the upper side i.e. dorsal side.
Characteristics-
Body Organisation:
- Echinoderms are triploblastic organisms with a unique pentaradial symmetry as adults, although they exhibit bilateral symmetry during their larval stage.
- Echinoderms have an organ-system level of organisation.
- They possess spiny skin, which gives them their name (echino = spiny, derm = skin).
- Echinoderms have a coelom (body cavity) and a unique water vascular system that aids in locomotion, feeding, and respiration.
- They lack a centralised brain but have a decentralised nervous system with nerve rings and radial nerves.
Locomotion:
- Echinoderms exhibit diverse modes of locomotion.
- Most echinoderms have tube feet, which are part of the water vascular system, and use them for slow crawling or attachment to surfaces.
- Some echinoderms, like sea stars, move by alternating the action of their tube feet and muscle contractions.
- Some echinoderms, such as sea cucumbers, can contract their bodies to move or use muscular contractions for limited crawling.
Reproduction:
- Echinoderms reproduce sexually, with separate sexes (male and female).
- Fertilisation is typically external, with the release of eggs and sperm into the water column.
- Echinoderms exhibit indirect development, where a larval stage called a bipinnaria or a brachiolaria develops into the adult form through metamorphosis.
Feeding Strategies:
- Echinoderms exhibit diverse feeding strategies depending on their ecological niche.
- Many echinoderms are scavengers or detritivores, feeding on decaying organic matter or small particles.
- Some echinoderms are herbivores, consuming algae or other plant material.
- Predatory echinoderms, like sea stars, use their tube feet to capture and feed on other invertebrates.
Examples:
Asterias (Star fish), Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (Sea cucumber) and Ophiura (Brittle star).
