Cassiopeia xamachana, the Blue Upside Down Jellyfish, also called the Mangrove Jellyfish, is named because its flattened bell rests upside down on the bottom. It extends its bluish tentacles up into the water where they capture plankton food and absorb light that it used via its photosynthetic zooanthellae algae that are housed in its body.

Found within the roots of mangroves in the Gulf of Mexico, Caribbean, and other tropical waters. It prefers wide sandy bottoms in the aquarium and requires high intensity light for photosynthesis to occur. It will not tolerate sudden changes in salinity or pH can have radical consequences.

Its sting can be slightly toxic. Care should still be taken though when handling it or while doing maintenance on the aquarium. It will require daily supplemental feeding with zooplankton substitutes.