Calcareous sponges take a wide range of shapes, including irregular massive forms, vase-shaped bodies on a stalk or meshworks of thin tubes. A common feature is the supporting skeleton, made of calcareous, star shaped structures - or spicules. These usually have three points, but some species have two or four pointed spicules. Reproduction may be both sexual and asexual, by budding. The eggs hatch to free swimming larvae which attach themselves to the bottom after a few days.