Jellyfish life cycle, artwork. At bottom right are a sperm (with tail) and egg (round). The sperm fertilises the egg to produce a planula, a small larva covered in cilia. This settles on a surface and develops into a polyp (bottom centre). After a growth phase the polyp begins reproducing asexually and immature jellyfish bud from it. These mature into adult jellyfish, or medusas (top centre). At top right is an enlarged view of a tentacle showing the mechanism by which nematocysts (stinging cells) are deployed.