1. True spongin is found only in members of the class Demospongiae. 2. Researchers have found over 100, 000 types of spongin . 3. Spicule density is high with little to no spongin present. 4. More commonly, the mesohyl is stiffened by spicules, by spongin fibers or both. 5. They are bleached and marketed; the spongin gives the sponge its softness and absorbency. 6. Spongin gives a sponge its flexibility.7. Sponge skeletons consist of either spongin or calcareous and siliceous spicules with some collagen molecules interspersed. 8. They are distinguished by a siliceous skeleton of two and four rayed spicules and contain the protein spongin . 9. Demosponges use spongin , and in many species, silica spicules and in some species, calcium carbonate exoskeletons. 10. Bath sponges can be defined as any sponge species possessing only spongin fibers which are springy fibres made from collagen protein.
