No germ layers in embryo. Cellular grade of organization. Physiological functions performed by individual cells. Osmoregulation in freshwater species by contractile vacuole. Larvae mobile and disperse using flagella.
Reproduction is asexual by budding, or sexual.
Most species hermaphroditic. Fertilization is internal. 5 - 8,000 species. Prepared slides of sections of sponges for choanocytes and spongocoel. Hydrostatic skeleton, or 'elastic' skeleton of mesoglea.