Encyclopedia of Science

[o1generallee4130]

Why is it that the outer layer is still referred to as the epithelial layer even though sponges lack tissues of any kind? Any help would be appreciative thanks.

[CynthiaA]

[quote="o1generallee4130"]Why is it that the outer layer is still referred to as the epithelial layer even though sponges lack tissues of any kind? Any help would be appreciative thanks.[/quote]

Pinacocytes are flat thin cells on the surface of a sponge. The pinacocytes form the pinacoderm of the porifina (sponge). The pinacoderm serve to function in some ways the same as skin. It is because of the similarity of function between skin and the pinacoderm the use of the term “epithelial” layer occurs. Epithelial layer is a way to explain the function of the pinacoderm by the similarity in function. It is a way to better understand HOW the pinacoderm works, not necessarily WHAT the pinacoderm actually is.

The pinacocytes have the ability to contract and allow the sponge to change shape. Some pinacocytes develop the ability to regulate water circulation. These special pinacocytes are referred to as porocytes. The pinacocytes and porocytes construct the pinacoderm, which is the leathery surface layer of porifina.