Respuesta :

They are one cell thick

Answer: Epithelial tissue is a very thin type of tissue.

Explanation:

Epithelial tissue is a very thin type of tissue found in mostly invertebrates ( example: Phylum Cnidaria) Organisms that possess this tissue typically don't require respitory systems. This is due to epithelial tissue being so thin that gases diffuse through it. This is how these organisms breathe, they exchange gas with their surrondings.  Gas diffuses right through their skin, and therefore they breath via diffusion.