Echinodermata overview
Echinoderms are a a large phylum made up of only marine animals. There are about 7,000 different species in the Echinodermata phylum. They are found usually on the sea floor in most marine habitats and in the ocean depths. Echinoderms usually are a wide variety of colors, all have symmetry, and a lot have over five arms. They have shells which are covered by skin. Three animals that fall in this category include sea stars, brittle stars, and sea cucumbers.
Sea cucumbers
Sea cucumbers extract oxygen from water by using a pair of respiratory trees that are near the anus. Basically the way that they breath is by drawing water in through the anus and then expelling it. The gas is exchanged through the walls of the tubules.
Brittle Stars
Brittle Stars are a creature that lives in the ocean and are similar to sea stars. The gas exchange inside of a brittle star occurs in sacs called bursae. There are around 10 bursae in each brittle star. Water flows through them by using the muscle contractions of cilia which help to move the water. It also uses the Hermal System, which is a series of sinuses and vessels that transport oxygen throughout the sea creature.
Sea Stars
Sea Stars (starfish) have an interesting way of respiring. The process occurs through the tube feet, and through the dots on the body which are called papillae. They reach through the muscular body wall and then to the water they are in. Oxygen from the water goes into and through the starfishes' body by the fluid in the main body cavity. Alike brittle stars, starfish also use the Hermal system to transport oxygen throughout the body.