∞ generated and posted on 2016.08.31 ∞
External embryonic tissue that gives rise to the outside of animal bodies as well as the nervous system.
Of the three primary germ layers that make up the tissues of early embryos, the ectoderm is that which is found on the outside. In a sense this tissue is what is there in the embryo making up the entire blastula or hollow-ball-of-cells stage, but in fact this tissue is considered to have "officially" differentiated into ectodermal tissue only upon gastrulation, i.e., the invagination that converts the blastula into the gastrula.
Cnidarians possess the least derived of ectodermal tissue found in animals while sponges lack ectodermal tissue though still possess a cellular epidermis.