Cytochemical studies of acid phosphatase in etching cells of boring sponges

Etching cells of boring sponges effect the excavation of calcium carbonate substrates by partial chemical dissolution. They are characterized by the same features found in active osteoclasts, the cells which effect bone resorption in vertebrates. These similarities include a region of numerous cell processes and a system of cytoplasmic bodies, vesicles, and vacuoles which are structurally connected with a tubular system and with extra-cellular channels (Pomponi, 1979). An extensive rough endoplasmic reticulum, Golgi complex, and lysosomes indicate that a lysosomal system is operative (Pomponi, 1979). The lysosomal system has been implicated as the primary mechanism in the destruction of calcined tissue by osteoclasts (Vaes, 1968; Hancox, 1972, Gothlin & Ericsson, 1976; Holtrop & King, 1977). Vaes (1968) proposed that acid hydrolases of lysosomes are active in the resorption of the organic matrix of bone.