Formation and construction of asexual buds of the freshwater spongeRadiospongilla cerebellata (Porifera, Spongillidae)

Abstract

The buds ofRadiospongilla cerebellata are formed asexually. Budding can be induced experimentally by injuring the sponge. The first sign of budding is a slight elevation of some surface areas, which proceed to rise rapidly so that they soon protrude conspicuously from the surface of the sponge. As a bud develops, the broad base joining it to the mother sponge narrows to a stalk, which finally breaks. The free buds drift in the water for 15–20 min and then settle, forming new sessile sponges. The buds, 1.5–2.5 mm in diameter, have an internal organization identical with that of the mother sponge. They are enclosed in a layer of pinacoderm perforated by dermal pores. Under the pinacorderm there is a shallow subdermal space, which is in communication with the incurrent canals leading to the choanocyte chambers. The water sucked into these chambers proceeds into the excurrent canal system and emerges from the sponge through the oscular tube. Spicules projecting radially from the bud bear apical tufts of microscleres. The skeletal spicules of the buds, like their choanocyte chambers, are smaller than those in the mother sponge. The chambers expand to their mature size by choanocyte mitosis. Buds and sponges are colored green by intracellular symbiotic algae of the genusChlorella.