![]() Gemmules survive hostile environments and can attach to a substrate and grow into a new sponge. A type of asexual reproduction found only in freshwater sponges occurs through the formation of gemmules, clusters of cells surrounded by a tough outer layer. ![]() Asexual reproduction is either by fragmentation (in which a piece of the sponge breaks off and develops into a new individual), or budding (an outgrowth from the parent that eventually detaches). Sponges reproduce both sexually and asexually. Gas exchange, circulation, and excretion occur by diffusion between cells and the water. The limit of this type of digestion is that food particles must be smaller than individual cells. Lacking a true digestive system, sponges depend on the intracellular digestive processes of their choanocytes for their energy intake. ![]() \): The sponge’s basic body plan is shown.ĭespite their lack of complexity, sponges are clearly successful organisms, having persisted on Earth for more than half a billion years. ![]()
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