Structures such as canals, chambers, and cavities enable water to move through the sponge to nearly all body cells. Since water is vital to sponges for excretion, feeding, and gas exchange, their body structure facilitates the movement of water through the sponge. Sponge larvae are able to swim however, adults are non-motile and spend their life attached to a substratum. Parazoans (“beside animals”) do not display tissue-level organization, although they do have specialized cells that perform specific functions. The simplest of all the invertebrates are the Parazoans, which include only the phylum Porifera: the sponges (Figure 1). The invertebrates, or invertebrata, are animals that do not contain bony structures, such as the cranium and vertebrae. Sponges are members of the Phylum Porifera, which contains the simplest invertebrates.
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