PENETRATION AND STORAGE OF SPONGE SPICULES IN TISSUES AND COELOM OF SPONGIVOROUS ECHINOIDS

When echinoids feed on sponges, silicate spicules of the sponge were f ound to enter their body either by penetration through the wall of the food canal into coelomic cavities or by penetration into skeletal pla tes and spines. The spicules. which have penetrated into the coelom, o bviously evoke a kind of protective answer. They were found to be enta ngled by clusters of cell remnants, the so-called brown bodies. The br own bodies contain melanin and gather at special sites of the echinoid body; these are the Stewart Organs, the gills and the inner side of t he ambulacral plates. Sometimes the silicate spicule becomes surrounde d by a calcareous sheath. The length of the sponge spicules makes thei r removal impossible, so that they are stored. The spicules penetratin g into the plates are partly incorporated into the stereom. The four s pecies examined in this study were Asthenosoma ijimai, Araeosoma owsto ni, Diadema setosum (collected in Sagami Bay, Japan in 1991) and Hapal osoma gemmiferum (collected in Suruga Bay, Japan in 1991).