![]() ![]() Since sponges are non-motile, they are typically found attached to rocks or other hard surfaces. ![]() To a lesser degree, some species have been known to feed on small crustaceans, like krill and shrimp. Sponges typically feed on bacteria, algae, and other tiny organisms in water. Water circulating through pores allows for gas exchange as well as food filtration. This is vital as sponges do not have a circulatory system, respiratory system, digestive system, muscular system, or nervous system as do many other animals. Their varied shapes (tube-like, barrel-like, fan-like, cup-like, branched, and irregular shapes) are structured to provide optimal water flow. Some giant sponges can reach heights of seven feet, while the smallest sponges reach heights of only two-thousandths of an inch. Sponges can be found at various depths in both marine and freshwater habitats and come in a variety of colors, sizes, and shapes. This interesting feature allows a sponge to filter food and nutrients from water as it passes through its pores. Sponge Parazoa Barrel Sponge - Parazoa Gerard Soury/Stockbyte/Getty Images Sponge parazoans are unique invertebrate animals characterized by porous bodies. They are composed of only four types of cells and have a simple body plan with just three cell layers. These tiny aquatic animals are flat, round, and transparent. Parazoa from the phylum Placozoa include the single species Trichoplax adhaerens. The three main classes of sponges include glass sponges (Hexactinellida), calcareous sponges (Calcarea), and demosponges (Demospongiae). Although multicellular, sponges only have a few different types of cells, some of which may migrate within the organism to perform different functions. They are aquatic organisms classified under the phylum Porifera with about 15,000 species worldwide. Parazoa is the animal sub-kingdom that includes organisms of the phyla Porifera and Placozoa. ![]()
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