Fig. 4
Ostia and porocytes in the pinacoderm. A Overview showing distribution of ostia with a range of sizes in the surface ‘tent’ of a sponge. B. Higher magnification shows the porocyte tightly adjacent to expinacocytes. C View of two ostia in a live sponge with amoebocytes crawling in the thin mesohyl between the two layers. D. Tearing of the epithelium during tissue preparation for SEM reveals that the porocyte is a flat cell that is anchored by tiny filopodia to the collagen layer just under the exopinacocytes. E. One porocyte can have several ostia. F. Ostia are ringed by an actin cytoskeleton. A,B,D,E: SEM; C: Differential interference microscopy; F, Fluorescence microscopy. Sp, spicule shaft; os, ostia; p, porocyte; exp, exopinacocyte; amb, amoebocyte; co, collagen