Epithelia separate the animal from its external environment. Do sponges have a true epithelium? What is a ‘true’ epithelium? We tested the integrity of the sponge epithelium using sponge tissue cultured (grown) on tiny membrane cups and recorded the resistance to the passage of ions across the epithelium (Transepithelial resistance). We found that the resistance of the freshwater sponge epithelium was as high as that of mammalian epithelia. Adams, Goss & Leys, 2010, PLoS One
If sponges do seal and maintain integrity, what are the molecules that allow them to do this? Are they different than those in other animals, and if so, do other animals also perhaps use the same techniques?