Acoelomates - Flatworms

In older taxonomy systems, the term Acoelomata was used to describe animal (more precisely, protostome) without continuous body cavity (coelom).



Acoelomates lack a fluid-filled body cavity between the body wall and digestive tract. This can cause some serious disadvantages. Fluid compression is negligible, while the tissue surrounding the organs of these animals will compress. Therefore, acoelomate organs are not protected from crushing forces applied to the animal’s outer surface. The coelom can be used for diffusion of gases and metabolites etc. These creatures do not have this need, as the surface area to volume ratio is large enough to allow absorption of nutrients and gas exchange by diffusion alone, due to dorso-ventral flattening.



According to some, acoelomates include the cnidarians (jellyfish and allies), and the ctenophores (comb jellies), platyhelminthes (flatworms including tapeworms, etc.), Nemertea, and Gastrotricha.



Flatworms (as seen in the model) have a body cavity filled with parenchyma (also called schiozocoel). The skin is formed from ectoderm while the intestine formed from the entoderm.

## Keywords
flatworms coelom