What is "spongin"

Spongin \Spon"gin\ (sp[u^]n"j[i^]n), n. (Physiol. Chem.) The chemical basis of sponge tissue, a nitrogenous, hornlike substance which on decomposition with sulphuric acid yields leucin and glycocoll.

n. A horny, sulfur-containing protein related to keratin that forms the skeletal structure of certain classes of sponges proteinaceous compounds of which the spicules in Demospongiae are composed.

Spongin, a modified type of collagen protein, forms the fibrous skeleton of most organisms among the phylum Porifera, the sponges. It is secreted by sponge cells known as spongioblasts.

Spongin gives a sponge its flexibility. True spongin is found only in members of the class Demospongiae. Researchers have found over 100,000 types of spongin.