The vast majority of sponges are heterotrophic filter feeders, meaning that they obtain their food by filtering water into a cavity of their body and extracting any organism that they can use for nutrition.  Sponges, Cryptotethya crypta, included used their specialized cells to carry out this filter, or suspension, feeding.

    In order for the sponge to carry out suspension feeding it needs to use its specialized cell types in unison.  It all begins with the choanocytes (or collar cells) using their beating flagella to create an inward current of water from outside the organism inward through the porocytes, or ostium, to the inner atrium, or spongocoel.  From there after, very small organisms and other nutritions material that was carried in is either taken up by archeocytes, or choanocytes who in turn transfer it to the archeocytes for digestion (as a side note, it has been observed that choanocytes and spicules have also contributed to the digestion of the filtered material).  Since sponges do not possess any muscles, nervous systems, or circulatory systems, they rely on their archeocytes to transport the nutrients throughout their body.  The filtered water is then released through the top of the sponge, or osculum.

    Sponges are primarily limited to feeding on small particles that can fit through its specialized porocytes.  Anything that flows in, including both organic and inorganic material is free game for the choanocyte and archeocyte absorption and digestion.  For the most part, with the size restrictions, sponges feed on small microorganisms including, but not limited to, algae and bacteria.  However, there are some carnivorous sponges that use their spicules to capture small crustaceans to eat.

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