Echinodermata

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).