What kind of digestive system does a sea star have?

Question

a simple or a complex?

and also, what kind of nervous system does it have??

none, rudimentary or developed ??

Answer 1

Starfish (also called sea stars) are any echinoderms belonging to the class Asteroidea. The names "sea star" and "starfish" are also used in a broader sense to include the closely related brittle stars, which make up the class Ophiuroide

The body cavity also contains the water vascular system that operates the tube feet, and the circulatory system, also called the hemal system. Hemal channels form rings around the mouth (the oral hemal ring), closer to the top of the starfish and around the digestive system (the gastric hemal ring). A portion of the body cavity called the axial sinus connects the three rings. Each ray also has hemal channels running next to the gonads.

Digestion and excretion

Starfish digestion is carried out in two stomachs: the cardiac stomach and the pyloric stomach. The cardiac stomach is a sack like stomach located at the center of the body and may be everted out of the organism's body to engulf and digest food. Some species are able to use their water vascular systems to force open the shells of bivalve mollusks such as clams and mussels by injecting their stomachs into the shells. With the stomach inserted inside the shell, the starfish is able to digest the mollusk in place. The cardiac stomach is then brought back inside the body, and the partially digested food is moved to the pyloric stomach. Further digestion occurs in the intestine. Waste is either excreted through the a**s on the aboral side of the body, or excreted through the mouth if the a**s is absent as in brittle stars.

Because of this ability to digest food outside of its body, the sea star is able to hunt prey that are much larger than its mouth would otherwise allow, including arthropods, small fish, and mollusks.

Some echinoderms live several weeks without food under artificial conditions. It is believed that they may receive some nutrients from organic material dissolved in seawater.

Sea stars and other echinoderms have endoskeletons, suggesting that echinoderms are very closely related to chordates; animals with a hollow nerve chord that usually have vertebrae.

Echinoderms have rather complex nervous systems, but lack a true centralized brain. All echinoderms have a network of interlacing nerves called a nerve plexus which lies within as well as below the skin. The esophagus is also surrounded by a number of nerve rings which send radial nerves that are often parallel with the branches of the water vascular system. The ring nerves and radial nerves coordinate the starfish's balance and directional systems. Although the echinoderms do not have many well-defined sensory inputs, they are sensitive to touch, light, temperature, orientation, and the status of water around them. The tube feet, spines, and pedicellariae found on starfish are sensitive to touch, while eyespots on the ends of the rays are light-sensitive.

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