Figure 1

The life cycle of the demosponge Amphimedon queenslandica . (A) Precompetent larvae emerge from maternal brood chambers (f) and then swim in the water column for a minimum of 4 hours before they develop competence to settle and initiate metamorphosis (a-b). Upon settling, the larva adopts a flattened morphology as it metamorphoses into a postlarva (c), which after 3 days of development displays most of the hallmarks of the adult body plan, including an aquiferous system with canals, choanocyte chambers and oscula (d). This settled postlarva will grow and mature into an adult sponge (e) with brood chambers housing embryos and larvae (f). (B) Cellular organization in the A. queenslandica adult. The interior of the adult sponge is an extensive aquiferous system with water canals (Ca) embedded in a collagenous mesohyl (M) and supported by siliceous spicules (Sp). Pinacocytes form the exopinacoderm and endopinacoderm, which line external surfaces and internal canals, respectively. Water canals are surrounded by choanocyte chambers (Ch) lined with flagellated choanocytes that filter surrounding seawater for food. Other cells in the sponge, such as amoeboid stem cell-like archaeocytes and vacuole-filled spherulous cells, are interspersed in the mesohyl. Sponge tissue section was stained with toluidine blue.