Cnidarians have an outer layer derived from ectoderm, an inner layer from endoderm, and a ____.

A) middle layer of mesoderm
B) watery middle layer
C) well-developed brain
D) jellylike matrix in between
E) complete gut

Mesoderm

The middle layer of an embryo in early development, which gives rise to muscles, bones, and the circulatory system among other structures.

Ectoderm

The outermost layer of cells or tissue of an embryo, giving rise to the outer skin layer, nervous system, and various sensory organs.

Endoderm

The innermost layer of cells or tissues of an embryo in early development, or the lining of the digestive and respiratory tracts in the mature organism.