Reasons why starfish don't need a heart?

Answer 1

Starfish have a well-structured system of tubes that works in lieu of the circulatory system. What passes for this circulatory system uses ocean water instead of blood. A starfish doesn't have a heart, but water running through the arms and feet provides oxygen.

Answer 2

Heart - no (at least not as you'd think of other animals with a heart - look up " starfish hemal system" if you want more info)

Blood - no (again, at least not as you'd think of other animals)

Rectum & anus - yes. Not all STARFISH have five arms? Some only have three, others six or seven, some twenty, and a few up to fifty arms! STARFISH have thousands of tiny, sharp spines covering them from the tip of one arm to the tip of the others? That is why starfish belong to a group of sea creatures called echinoderms. Echino means "spiny," and derm means "skin." These spines protect starfish from tiny sea creatures that try to attach themselves to them and feed off their strength. A STARFISH'S mouth is on the bottom of its body, right in the center? STARFISH have very small feet called tube feet? Each tube foot has a tiny suction cup at its tip. Starfish use these suction cups to walk and also to pump in oxygen-so starfish actually breathe through their feet! STARFISH do not have eyes? Instead, at the end of each starfish arm are many cells that are very sensitive to light. As a starfish travels slowly through the water, these special cells and the sensitive tube feet help the starfish find food. STARFISH eat oysters? When an oyster senses that a starfish is near, it will quickly close its shell with a snap! But the starfish wraps its arms around the shell and uses the suction cups on its tube feet to pry the oyster's shell open just a crack. A STARFISH actually pulls its stomach out through its mouth to eat? Because the oyster's shell only opens as wide as a piece of cardboard, the starfish must slip its stomach into the shell and eat the oyster while it is still in its closed shell. When a STARFISH loses its arms in an accident, it will grow new ones? One kind of starfish can grow an entire body from a piece of its arm one-half inch long! The reason they do not have a heart is because they don't have blood to pump aroung their bodys. Instead they use sea water to pump around their bodies. The water vascular system uses cilia and the constantly contracting ampullae to keep things moving. An ionic imbalance causes water to flow into the madreporite, entering the water vascular system. Some of this water is diverted into the periviscerial coelom (the large cavity in which major organs are suspended), where it is circulated by the beating of cilia. Most oxygen enters the starfish via diffusion into the tube feet (with the water vascular system), or the papulae (small sacs covering the upper body surface.

Answer 3

Echinoderms are characterized by radial symmetry, several arms (5 or more, mostly grouped 2 left - 1 middle - 2 right) radiating from a central body (= pentamerous). The body actually consists of five equal segments, each containing a duplicate set of various internal organs. They have no heart, brain, nor eyes, but some brittle stars seem to have light sensitive parts on their arms. Their mouth is situated on the underside and their anus on top (except feather stars, sea cucumbers and some urchins). Echinoderms have tentacle-like structures called tube feet with suction pads situated at their extremities. These tube feet are hydraulically controlled by a remarkable vascular system. This system supplies water through canals of small muscular tubes to the tube feet (= ambulacral feet). As the tube feet press against a moving object, water is withdrawn from them, resulting in a suction effect. When water returns to the canals, suction is released. The resulting locomotion is generally very slow.