Porifera

Porifera are sponges.  These are usually marine animals that live fixed to rock surfaces.  Because they are not mobile they are known as sessile or sedentary.   Sponges are tubular with a hollow inside known as their gastrovascular cavity.  Although they look like they’re perfectly round they are not. They are asymmetrical. 

Water from the surrounding environment enters the porifera as gastrovascular cavity by way of many small pores.  The waterThe universal solvent essential for life. is moved through the gastrovascular cavity by cellsThe basic structural and functional units of life. call choanocytes that have flagellaLong, whip-like structures used by some cells (e.g., sperm) for movement. or little tails with rotary motion.  These flagella wave in an effort to move water through the sponge and out the top.  In contact with a choanocyte is an amoebocyte which is a cell that will absorb food particles.  As water moves through the gastrovascular cavity, food particles get trapped by the choanocyte and absorbed by the amoebocyte.  Although there are two distinct cell types in sponges, they are not considered as having true tissues, and certainly no organs.

Sponges are known as filter feeders in the marine environment.  They can also be called suspension feeder.  Either name you want, sponges filter particles of food suspended in the water column.  There are other marine filter feeders, like baleen whales and tube worms.  The baleen is like a feathery tooth. The Swiffer duster attachment on tube worms increases the surface area of the feeding appendage, making it more efficient.