Digestion and Respiration
Most sea stars are carnivorous. They feed by extending part of their stomach inside out through the mouth to envelop the food. The stomach then secrets digestive enzymes produced by large digestive glands that extend into the arms. The digested food is then carried into the glands for absorption and the stomach is pulled back into the body. The intestines are short or missing entirely.
Brittle stars lack an anus.
The gut of a sea urchin or sea cucumber is long and coiled. In sea urchins, this is an adaptation that is needed for the longer digestive period needed for the breakdown of plant material. A long gut is also needed by sea cucumbers because they must take in large amounts of sediments to obtain enough organic matter.
All echinoderms transport nutrients in the fluid that fills the entire body cavity. This fluid is called coelomic fluid. The coelomic fluid also transports oxygen because most echinoderms lack a distinct circulatory system. In sea stars and sea urchins, gas exchange takes place across branched projections of teh body wall connected at the base to the coelomic cavity. In sea cucumbers, water is drawn in through the anus to a pair of branched tubes called respiratory trees. The respiratory trees are extensions of the gut and are suspended in the body cavity and surrounded by the coelomic fluid allowing considerable gas exchange.
Brittle stars lack an anus.
The gut of a sea urchin or sea cucumber is long and coiled. In sea urchins, this is an adaptation that is needed for the longer digestive period needed for the breakdown of plant material. A long gut is also needed by sea cucumbers because they must take in large amounts of sediments to obtain enough organic matter.
All echinoderms transport nutrients in the fluid that fills the entire body cavity. This fluid is called coelomic fluid. The coelomic fluid also transports oxygen because most echinoderms lack a distinct circulatory system. In sea stars and sea urchins, gas exchange takes place across branched projections of teh body wall connected at the base to the coelomic cavity. In sea cucumbers, water is drawn in through the anus to a pair of branched tubes called respiratory trees. The respiratory trees are extensions of the gut and are suspended in the body cavity and surrounded by the coelomic fluid allowing considerable gas exchange.