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Phylum Cnidaria > jellyfish > Class Scyphozoa > Order Rhizostomeae
Upsidedown jellyfish
Cassiopea sp.
Family Cassiopeidae
updated Dec 2019
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. And also in the submerged reefs nearby. It is also seen on some of our other Southern shores.

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.

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

Upper side.
Pulau Semakau, Mar 08

Turning around.

Upside down.
Farm in its arms: 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, Nov 07

Closer look at the underside.

Upsidedown jellyfishes on Singapore shores
On wildsingapore flickr

Other sightings on Singapore shores

Changi Lost Coast, Jun 22
Shared by Richard Kuah on facebook.

Sentosa Tg Rimau, Jan 22
Shared by Loh Kok Sheng on facebook.

Sentosa Tg Rimau, Nov 21
Shared by James Koh on facebook.

Kusu Island, Sep 09
Shared by James Koh on his blog.

Kusu Island, Apr 17
Shared by Marcus Ng on facebook.

Upside down.
Pulau Semakau, Nov 07

Upside down.
Terumbu Semakau, Nov 12

Terumbu Raya, Jul 09
Photo shared by James Koh on his blog.

Pulau Semakau East, Jan 16
Shared by Marcus Ng on facebook.

Beting Bemban Besar, Apr 10
Shared by Loh Kok Sheng on his flickr.

Seringat-Kias, Nov 2019

upside-down jellyfish from SgBeachBum on Vimeo.

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

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