Sponges The skeleton of sponges consists of microscopic calcareous or siliceous spicules. The demosponges include 90% of all species of sponges. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. Where spicules of silica are present, they have a different shape from those in the otherwise similar glass sponges..
SponGEs ThE sKeLETOn of SpONGes coNSiSTs OF microscopic calCareoUs Or SiLiceous sPiCules. the demOSPongEs InclUdE 90% of alL SpecieS oF spONGes. tHeiR "SkELetonS" ARE mAde Of SpicuLEs cONsIstiNG of FIBeRS of tHE proTein spongIn, tHE miNeral siliCa, or boTh. wherE SpicuLes oF siLica are presenT, tHEY haVE a DiFferENT shapE fROm ThoSe in the OtHerwIsE SimiLar gLaSS spoNgEs..