Describe the different classes of echinoderms using examples.

Echinoderms are divided into the five classes: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lillies or feather stars) and Holothuroidea (sea cucumbers)

Explanation:

The term Echinoderms is derived from the latin word Echinodermata (name of the phylum) that includes star fish and sea urchins from Greek ekhinos "sea urchin" originally "porcupine, hedgehog" (see echidna) + derma means skin so called from its spiky shell.

Charactersitic features of Echinoderms:

They are exclusively marine The larval forms show bilateral symmetry and adults show radial symmetry They are triploblastic They have a true coelum the body is uniquely shaped It exhibits organ system grade of organisation

Echinoderms don't have brain they have nerves running from mouth into each arm or along the body. They have a shell made up of calcium carbonate which is covered by skin. They get their food and oxygen for energy. They use tube feet to obtain from water. The tiny tube feet are involved in passing collected food towards the central mouth. These animals are detritivores performing similar functions to earthworms on earth on land in recycling nutrients.

There are five classes of echinoderms:

Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lillies or feather stars) and Holothuroidea (sea cucumbers)