Box Jellies: Cubozoa

Because box jellies can see, they are difficult to study because they react to the presence of their human observers by swimming away. Box jellies are active swimmers capable of moving 10 to 20 feet (3 to 6 meters) per minute. They move toward light and are active during the day and night, although they may feed only during the night or predawn hours.

The life history of box jellies has two stages: bottom-dwelling polyp and freely swimming medusa. A polyp (PAH-luhp) is a body type that consists of a tubular sac with a mouth and tentacles on the top. The medusa (mi-DOO-suh) is the tentacled, jelly-like, umbrella-shaped body form. The eggs and sperm from male and female medusae (mi-DOO-see, the plural of medusa) are released into the water and combine outside the body to form a larva (LAR-vuh), or early stage of the animal that changes form before becoming an adult. The larva settles on the bottom and becomes a polyp. The entire polyp of a box jelly becomes the young medusa.