General Topics of Phylum Echinodermata

Tube Feet

Tube feet are connected internally with ambulacral or water vascular system. Each tube foot has an ampulla, a podium and a sucker. Ampulla additionally possesses circular muscles. Tube feet are sensory structures that take part in adhesion, locomotion, respiration and food capturing.

Ambulacral/Water Vascular System

It is a system of canals that circulates water in the body of an echinoderm and is connected with its tube feet for their expansion and contraction  through hydraulic force. It is a modified part of coelom. It is connected to the outside through a perforated plate known as madreporite. A stone canal occurs between the two. The system mainly helps in locomotion,  respiration, adhesion and food capturing.

Star Fish

Star-shaped body bearing short spines all over. It has mouth and ambulacral grooves containing tube feet on the lower (oral) side, and anus and madreporite on the upper (aboral) side.

Dermal branchiae protrude through minute pores in the integument on the aboral surface. They carry on respiration and excretion.

Small pincer-like pedicellariae occur on the oral as well as aboral surface. They keep the body surfaces clear of debris and organisms by their movements.

A tentacle and an eye lie at the tip of each arm. Dried and powdered starfishes form a calcium rich fertilizer. Starfish eggs are edible. They cause a great damage to the clam and oyster beds.

Sea Urchin

Omnivorous. It moves with the help of spines.

The body is globular with long, pointed movable spines. Pedicellariae are present among the spines.

The mouth is present in the centre of oral surface. The sea urchin has a masticatory apparatus, called Aristotle’s Lantern. It is formed by five strong and sharp teeth. Its teeth are used for feeding.

Fig. Representatives of the living classes of Echinoderms