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The upside-down (or mangrove) jellyfish, Cassiopea, is a large jellyfish (up to about 30 cm in diameter) that is brown or olive and creamy white in color. Its underside is covered with extensions (oral arms) that branch into thousands of lacy extensions (lappets). These lappets contain thousands of photosynthetic yellow-brown zooxanthellae (mutualistic photosynthetic dinoflagellate algae). The lower margin of the bell is surrounded by multibranched tentacles. Cassiopea swims in the typical jellyfish orientation, with its mouth facing downward. However, unlike most jellyfish, Cassiopea is seldom seen swimming, instead spending much of its time flipped upside down, pulsating, on sandy or muddy substrates in mangrove or soft bottom bay habitats. This orientation provides its photosynthetic zooxanthellae with critical access to light (Kaplan 1988; Fitt and Costley 1998).