Upside-down Jellyfish

Cassiopeia xamachana

Web page created by Ku Miyagawa

Classification: The Upside-down Jellyfish belongs to Phylum Cnidaria, which includes other jellyfish, coral, and sea anemone. It is an invertebrate animal, which lucks backbones. There are two common upside-down jellies in Florida, such are Cassiopea frondosa and Cassiopea xamachana.

Appearance: The Upside-down Jellyfish often lies mouth upwards on the bottom of  the calm shallow water, pulsating its bell, and its lips as it wafted by. It is usually 12 to 14 inches diameter, yellow or brown colored by the algae, which lives within the tissues of the medusa. However, the Juvenile Upside-down Jelly starts its life as free-swimming, and as soon as it reaches 1 inch, it inverts its bell and often pulsates to the bottom of water where it lands upside-down, its oral mouth upward. Because it usually lies on the bottom of the water, it is often mistaken as sea anemone.

Body: The body of the jellyfish is consisted of 95% water, 3% salt, 2% protein. It is an invertebrate animal with a simple nerve net, which is used as a brain to taste, sense and smell. It is a triproblastic animal that has the rapid canals, which carry nutrients, on its bell. It also has a large body cavity; unlike other jellyfish, however, the Upside-down Jelly has no central mouth. Instead, it has more than 40 openings of mini-mouth along mouth arms that form canals. The bell also works as a suction cup, which prevents the animal from being swept away by currents.

Range: The Upside-down Jellyfish is commonly found in the Caribbean, Hawaii, and along the coast of Southern Florida.

Habitat: The species is found in a wide variety of tropical water environment. Shallow lagoons, inter tidal sand banks or mud flats, and  mangrove swamps. Because of the zoothanthellae, which lives within the mouth arms produce oxygen as well as sugar, the Upside-down Jellyfish is capable of living in low oxygen concentration.

Prey: As other jellyfish, the Upside-down Jellyfish feeds on small drifting animal called, zooplankton such as other jellyfish and juvenile fish. However, the Upside-down Jellyfish also feed upon the zooxanthellae, the symbiotic dinoflagellate algae that provides sugar to the jellyfish. The zooxanthellae lives in the tissues on the ventral surface of the jellyfish, and that is why the Jelly is "upside-down", to provide sunlight efficiently for the photosynthetic algae. In fact, one species lives in the blackish lagoons of Turk, in the Caroline Islands of the Pacific, has become so specialized that it no longer needs nematocysts to catch prey.
     On the other hands, the jellyfish is mainly eaten by the Ocean Sunfish (Mola mola) and the Leatherback Sea Turtles.

Reproduction: The jellyfish is dioceous; an adult female jellyfish produce eggs and holds them around her mouth until a male jellyfish release his sperm into the water, and the female uses her oral arms and tentacles to bring in the sperm into the water.

Life Cycle of Jellyfish:

Stinging Facts: Like other jellyfish, the Upside-down Jellyfish also holds cnidocytes in both epidermis and gastrodermis, which is used for protection and capturing of food, may result in painful experience. The stinging of the Upside-down Jellyfish is considered to be the moderate to severe pain to man. It may result in skin welts, skin rash, itching, vomiting and skeletal pains. If one is stung by the jellyfish,  s/he should (1) Wash in sea water. (2) Remove tentacles if possible. (3) Apply alcohol. (4) Pour dry flour, baking soda (5) Scrape the caked material with a knife. (6) Reapply. (7) Rescrape. (8) If serious, seek emergency medical aid. (Campbell 117)

Related Links:


 1. Campbell, George R. An Illustrated Guide to Some Poisonous Plants and Animals of Florida. Englewood, FL: Pineapple, 1918.

 2. Marshall Cavendish. International Wildlife Encyclopedia. Vo. 12. New York: Marshal Cavendish, 1990.

3. Waller, Geoffrey, ed. SeaLife: A Complete Guide to the Marine Environment. Washington: Smithsonian Institution, 1996.

4. Walls, Jerry G. ed. Encyclopedia of Marine Invertebrates. New Jersey: T.F.H Publications, 1982.

5. "Characteristics of Class Scyphozoa." Phylum Cnidaria.<>. (20 March 2000).

6. "Jellies: Upside Down Jelly." Tennessee Aquarium. <> (20 March 2000).

7. "Jellyfish." National Aquarium in Baltimore.<> (20 March 2000).

8. Marine Aquarium Society of Los Angels. "Jellyfish." Jellyfish Information. <> (20 March 2000).

9. Villoch, Carlos. "Magic Sea: Stock Photography and Fine Art Prints." Magic Sea Stock Photography.<> (20 March 2000).

10. "Welcome to the JellyCam." JellyCam.<> (20 March 2000).