Pictures found in: Sea star
Digestive System: The digestive system of a sea star is quite complex, with its mouth on its underside and anus on the top. They feed by everting, part of their stomach inside out through the mouth to envelop the food. The stomach then secretes digestive enzymes produced by large digestive glands that extend into the arms. The digested food is carried into the glands for absorption and the stomach pulled back inside the body.
Circulatory System: Sea stars do not have a circulatory system.
Nervous System: Sea stars have a network of nerves that coordinates movements of tube feet and spines in the absence of a brain.
Excretory System: There is no formal excretory system present in sea stars.
Reproductive System: Sea stars reproduce by means of broadcast spawning where the males and females discharge there eggs and sperm into the water where they are fertilized.
Integumentary System: The integumentary system of a sea star consists of five arms and spines or bumps all over its body. The spines are protective and also help with respiration.
Body Plan: Unlike many organisms, the sea star and the rest of its echinoderm family have a pentamerous radial symmetry and also lack a head. They have no anterior or posterior end or even a dorsal or ventral side. It is useful to refer to one of its surfaces as oral, because that is where the mouth is located, and an opposite side - referred to as aboral. They also have an endoskeleton similar to humans, that is secreted within the tissues, rather than externally.
Sea stars live in temperate and tropical waters. Some are bottom dwellers while many live mostly in shallow marine environments. They eat scraps of food, algal mats, or even deceased organisms. Others are active predators that will attack and eat clams, snails, sponges, corals, anemones.
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