The Upside-Down Jellyfish (Cassiopea ornata) is a marine (saltwater) planktonic scyphozoan in the Cassiopeidae family of upside-down jellyfish. It is a cnidarian. It is also known as the Sunbathing Jellyfish. 

It is a photosynthetic jellyfish. It is the only jellyfish that rests with its bell or umbrella on the ocean floor and its tentacles pointing upwards. It does this to receive light so that the symbiotic algae living on it can produce carbohydrates for the jellyfish to use as food for energy. 

The Upside-Down Jellyfish has a variety of colours, but is mainly white, blue, green, or brown. It has short tentacles. It has a bell-shaped dome with no eyes. Instead, it has light sensing organs called ocelli. It is composed of 95% of water, which enables it to float.

It grows up to 15 centimetres (6 inches) long.

It is found throughout the Indian and Pacific Oceans, especially in the waters of Australia, Guam, the Philippines, Japan, Indonesia, and Papua New Guinea. It prefers warm, shallow water in lagoons, canals, and in sandy areas around mangroves.

It uses photosynthesis, produced by algae, for its energy. It supplements this by catching floating creatures in its stinging tentacles. 

The Upside-Down Jellyfish is gonochoric, which means that it can reproduce sexually and asexually. When it is in medusa form, it reproduces sexually – i.e. the male fertilizes the female’s eggs when they are in the water. When it is in polyp form, it reproduces asexually – i.e. by budding (similar to a plant). 

Location of photographs: Sea Life London Aquarium, England 

Photographer: Martina Nicolls

Martina Nicolls: SIMILAR BUT DIFFERENT IN THE ANIMAL KINGDOM