Some sponges release their larvae, where others retain them for some time. The sperm are then transported to eggs, fertilization occurs and the zygotes develop into larvae. Sperm are frequently released into the water, where they are captured by sponges of the same species. Most sponges that reproduce sexually are hermaphroditic and produce eggs and sperm at different times. Freshwater sponges often produce gemmules prior to winter, which then develop into adult sponges beginning the following spring. Sponges that reproduce asexually produce buds or, more often, structures called gemmules, which are packets of several cells of various types inside a protective covering. Sponges reproduce by both asexual and sexual means. The flow of water through the sponge is unidirectional, driven by the beating of flagella, which line the surface of chambers connected by a series of canals. Cells in the sponge walls filter food from the water as the water is pumped through the body and out other larger openings. Sponges have tiny pores in their outer walls through which water is drawn. As sponges don't have mouths, they must feed by some other method. Sponges are characterized by a feeding system unique among animals. For example, some cells control the flow of water, in and out of the sponge, by increasing or decreasing the size of the pores. Sponge cells perform a variety of bodily functions and appear to be more independent of each other than are the cells of other animals. Other animals, including humans, have tissue-level organization because they have tissues with specific functions. Instead, their bodies are made up of specialized cells (cell-level organization) that do specific jobs. In fact, sponges do not even have true tissues. This is because sponges evolved much earlier than other animals. Internally, they do not have brains, stomachs, or other organs. You might think that sponges don't look like animals at all. \): The sponges often have tube-like bodies with many tiny pores.
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