Answer:
a. inner and outer cell layers separated by a jelly-like mesoglea.
Explanation:
The body wall of cnidarians and ctenophores consist of a inner and outer cell layers separated by a jelly-like mesoglea. The function of this mesoglea offer an hydrostatic skeleton to the Cnidarians.
The mesoglea is composed of several substances including fibrous proteins, like collagen and proteoglycans but in both cnidaria and ctenophora, the mesoglea contains muscle bundles and nerve fibres.
