Jellyfish: Scyphozoa

Physical characteristics: The swimming bell of a nightlight jellyfish usually is less than 3.5 inches (9 centimeters) in diameter. It has a bumpy surface caused by clusters of stinging cells, which give a purple or yellowish color to the bell. Four long oral arms and eight long tentacles alternate with eight sense structures in the spaces between folds on the bell. There is no polyp stage.

Geographic range: Nightlight jellyfish live in the Atlantic and Pacific oceans and in the Mediterranean Sea.

Habitat: Nightlight jellyfish live in surface waters of the open ocean but sometimes are carried on the current into shallow coastal waters.

Diet: Nightlight jellyfish eat animal plankton.

Behavior and reproduction: The medusae of nightlight jellyfish emit a blue-green light when they are touched or injured. Mucus released from the damaged area continues to glow, so that at night the The medusae of nightlight jellyfish emit a blue-green light when they are touched or injured. Mucus released from the damaged area continues to glow, so that at night the jellyfish look like glowing balls. (Illustration by Joseph E. Trumpey. Reproduced by permission.) jellyfish look like glowing balls in a boat's wake. Nightlight jellyfish do not have a polyp stage. The larvae develop without ever settling on the bottom.

Nightlight jellyfish and people: Nightlight jellyfish have a painful sting, which can cause a severe reaction.

Conservation status: Nightlight jellyfish are not threatened or endangered. ∎