approximately how many species of sponge live in fresh water environments
Marine life Sponges are similar to other animals in that they are multicellular, heterotrophic, lack cell walls and produce sperm cells. Unlike other animals, they lack true tissues and organs, and have no body symmetry. The shapes of their bodies are adapted for maximal efficiency of water flow through the central cavity, where it deposits nutrients, and leaves through a hole called the osculum. Many sponges have internal skeletons of spongin and/or spicules of calcium carbonate or silicon dioxide. All sponges are sessile aquatic animals. Although there are freshwater species, the great majority are marine (salt water) species, ranging from tidal zones to depths exceeding 8,800 m (5.5 mi).
Sea urchin Population densities vary by habitat, with more dense populations in barren areas as compared to kelp stands.[36][37] Even in these barren areas, greatest densities are found in shallow water. Populations are generally found in deeper water if wave action is present.[37] Densities decrease in winter when storms cause them to seek protection in cracks and around larger underwater structures.[37] The shingle urchin (Colobocentrotus atratus), which lives on exposed shorelines, is particularly resistant to wave action. It is one of the few sea urchin that can survive many hours out of water.[38]