Sponges<span> are </span>animals<span> of the </span>phylum Porifera<span> (</span><span>/<span>pɒˈrɪfərə</span>/</span><span>; meaning "pore bearer"). They are multicellular organisms that have bodies full of pores and channels allowing water to circulate through them, consisting of jelly-like </span>mesohyl<span> sandwiched between two thin layers of</span>cells<span>. Sponges have unspecialized cells that can </span>transform into other types<span> and that often migrate between the main cell layers and the mesohyl in the process. Sponges do not have </span>nervous<span>, </span>digestive<span> or </span>circulatory systems<span>. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes</span>
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).
