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Phylum Cnidaria > jellyfish > Class Scyphozoa > Order Rhizostomeae
Upsidedown jellyfish
Cassiopea sp.
Family Cassiopeidae
updated Mar 13

Where seen? This topsy turvy jellyfish can be seasonally common on Pulau Semakau, found throughout the intertidal from the seagrass meadows to the reef flats.

Features: Bell about 4-12cm, with short stout branched oral arms. The oral arm length about half the diameter of the bell. There is usually a pattern of white bars on the upper and underside of the bell.

The animal prefers to be 'upside down', with its bell facing the sea floor and oral arms facing upwards toward the light. When one is turned the 'right' way up, it will slowly turn itself upside down again.

In its preferred position, with only its oral arms visible and bell hidden, it is sometimes mistaken for a sea anemone.

The jellyfish harbours microscopic, single-celled algae (called zooxanthellae) inside its body. The algae undergo photosynthesis to produce food from sunlight. The food produced is shared with the jellyfish, which in return provides the algae with shelter and minerals. It is the algae which gives the jellyfish its colours. Because it relies on photosynthesis, the jellyfish tends to be found in shallow waters.

Pulau Semakau, Mar 08

Turning around.

Upside down.
Pulau Semakau, Nov 07

Upside down.
Terumbu Semakau, Nov 12

Upside down.

Pulau Semakau, Nov 07

Upsidedown jellyfishes on Singapore shores
Photos for free download from wildsingapore flickr
Distribution in Singapore on this wildsingapore flickr map

video clips and more photos of upside-down jellyfish on Singapore shores

With grateful thanks to Dr Michael N Dawson of the University of California, Merced for identification of this jellyfish.

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