What is a young jellyfish called?

When people think of jellyfish, they usually picture a gelatinous marine animal with a bell-shaped body and long tentacles. While accurate, that mental image depicts only the final stage of a jelly's life - the "medusa" phase.

Jellyfish are not true fish, but invertebrates. They do not have bones, brains, or hearts. There are over 2,000 known species of jellyfish, and scientists believe there could be as many as 300,000 more species yet to be discovered. They can be found in every ocean of the world, and range in size from 0.5 millimeters (1/32 in) to nearly 2 metres (7 ft) wide, with tentacles over 36 m (119 ft) long. Their tentacles are used both for defense and to stun their prey before eating.

To reproduce, in most species, the male and female jellyfish release large amounts of sperm and eggs into the ocean around them; the eggs are fertilized and drift along. The developing eggs, now known as larvae or planulae, eventually settle downward, attach to a firm surface, and become polyps. At the polyp stage, jellies resemble tiny anemones and continue to grow. When conditions are right, the polyps begin asexual reproduction via a process called “strobilation”. The polyp forms layers, then releases cross-sections of itself into the water. These floating cross-sections, complete tiny jellyfish, are called ephyrae. Within a few weeks, the ephyra matures. Once a bell appears, it is considered to be a medusa, capable of reproduction, starting the whole process over again.