Polycladida
Polycladida which is also known as marine flatworms do not have circulatory and respiratory organs. Hence, in order for them to survive, the exchange of gas takes place in the form of simple diffusion; Oxygen and nutrients pass through their bodies and Carbon dioxide is able to leave all parts of the body. Therefore, many of the flatworms have flat ribbon-like or leaf-like shapes like the one in the picture above so as to have larger surface area to volume ratio, allowing diffusion to occur at a faster rate.
Monday, April 7, 2014 · 7:36 AM · 0 comment(s).