Porifera morphology and internal structure. A. "Callyspongia (Callyspongia) samarensis" (Demospongiae: Haplosclerida), Ternate, Maluku province, Indonesia (photo N.J. de Voogd); B. SEM image of cross section of mesohyl of the demosponge "Scopalina ruetzleri" obtained by freeze-fracturing technique (courtesy L. de Vos); C. Detail of choanocyte chamber of "Scopalina ruetzleri" (courtesy L. de Vos).