Siliceous particles incorporation in Chondrosia reniformis (Porifera, Demospongiae)

A different reactivity of the demosponge Chondrosia reniformis pinacoderm w ith regard to crystalline and amorphous silica is described. Following the crystalline quartz particle settlement, the pinacoderm breaks and exopinaco cytes contract to form a rim around this foreign material that becomes grad ually incorporated. Instead, amorphous opaline spicules elicit a motile res ponse of exopinacocytes. At the onset of this process they lay a thin homog eneous matrix on the spicule, while afterwards several exopinacocytes join together forming a cellular coat covering the spicule. The sinking of both kinds of foreign material is allowed by the malleable organization of the c ollagenous ectosome. The effect of different silica crystalline forms on sp onge cells is discussed by considering similar phenomena in other animals.