Jellyfish belong to the Cnidaria group, which encompasses animals whose mouths are surrounded by stinging tentacles, like corals and sea anemones.
This stinging power is the result of cells that, at the slightest touch, open up and release their contents : a harpoon that scratches the victim’s skin, infected with venom by a filament.
The jellyfish breed in two successive phases. The first is sexual, involving spermatozoa and ova. The two come together to form an egg, and later a larva with cilia. The larva lives for a while in the open water before attaching to a surface. The second phase is asexual.
It begins when the larva attaches to a surface so that it can develop into a polyp, a sort of small anemone just a few millimetres in size. It can divide to create a new polyp or segment itself and become a strobila, which looks something like a stack of plates and, at maturity, releases tiny jellyfish called ephyra.
The jellyfish feed on plankton that they catch with their stinging tentacles. Some specimens can reach up to 50 cm in diameter.
Medusa is not just another name for jellyfish. It was also the name of a beautiful sea deity who was proud of her hair. To punish her for her vanity and for coupling with Poseidon, Athena transformed her into a frightening monster, with boar's teeth, hair made of snakes, and eyes that would turn anyone who looked at her into stone.
