Integument, Variations among vertebrates

The vertebrates belong to the phylum Chordata and are closely related to a small, fishlike, almost transparent invertebrate called amphioxus. Amphioxus represents chordate integument at its simplest: an epidermis, consisting of one layer of columnar or cuboidal epithelial cells and scattered mucous cells, covered by a thin cuticle, and a thin dermis of soft connective