Describe the Phylum Echinodermata in details?
The Phylum Echinodermata takes its name from two words of Greek origin: "echino," ; which means "prickle" or "spine," and "derma," ; which means "skin." All of these animals live in the ocean, and their names are familiar to us as the starfish, sand dollars, sea urchins, brittle stars, and sea cucumbers. While the adults certainly appear to have radial symmetry, their immature larval forms have bilateral symmetry, which places them, evolutionarily speaking, with other bilaterally symmetrical animals.
Echinoderms have several major features that set them apart from other deuterostomes like birds, reptiles, fishes, and mammals. Their bodies are partitioned into five parts (as in five-armed starfish), and lack segmentation into a brain and/or a head region. Although they also lack a central nervous system, echinoderms do have sensory organs that enable them to respond to stimuli. Their rough outer body covering is actually a skin that covers an endoskeleton made of calcium plates called ossicles.
Another distinguishing feature Echinoderms have is their water vascular system, which operates their tube feet. Echinoderms have a system of many muscular tube feet with suckers on the bottom that enable them to move by changing the water pressure. The tube feet operate much like an eye dropper bulb that, when squeezed and released, produces a suction, which attaches each foot to a surface.
The water vascular system of Echinoderms consists of a ring canal, which surrounds the mouth and feeds into radiating canals that extend into each of the five arms. Seawater is pumped into an opening called a madreporite, which is located off center on the top of the body disc.
Echinoderms such as the sea stars and the brittle stars have the ability to regenerate lost body parts. They reproduce externally by releasing sperm and eggs into the water, where fertilization occurs, along with the subsequent development of the zygote into free-swimming larvae.
Living Echinoderms are grouped into five Classes.