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Cassiopea frondosa, commonly known as the upside-down jellyfish, is a member of the class Scyphozoa within the phylum Cnidaria. It has also been called Polyclonia frondosa (Fewkes, 1883). Its color can vary from amber-yellow, olive, and greenish (Mayer, 1910). C. frondosa can range in size from 10-13 cm, but it has been noted to reach a maximum size of 27 cm (Humann, 1992). The bell is flattened to facilitate resting the top of the bell on the ground (Humann, 1992). Its oral arms are shorter than the diameter of the bell and are covered in small leaf-shaped projections (Perkins, 1908). The optimum temperature for C. frondosa, based on the number of bell pulses, is from 28.5 to 32.5 C (Mayer, 1914).
Cassiopea frondosa can appear along Florida, the Bahamas and throughout the Caribbean. It prefers sandy flats and shallow areas in mangrove and reef lagoons (Humann, 1992). It occasionally can be washed out towards reefs as well (Humann, 1992). Like corals, C. frondosa receives some nutrients from the symbiotic zooxanthellae growing within its tentacles (Humann, 1992). C. frondosa gets its common name from its orientation when sitting on the bottom of flat areas (Humann, 1992). In order to promote zooxanthellae growth, the jellyfish orients itself so that its tentacles face upwards towards incoming sunlight (Humann, 1992). It can be found at depths from 0-7 m, which also helps to promote zooxanthellae growth (Humann, 1992). Though they receive some sustenance from the algae within their tissues, C. frondosa is carnivorous and feeds upon plankton and other invertebrates floating in the water (Mayer, 1910). As they lie on the substrate they slowly pump their bell to create a flow of water over their tentacles and mouth in order to trap prey (Mayer, 1910).
During reproduction, the eggs remain at the small openings, or vesicles, on the surface of the oral disk until they have developed into planular larvae, at which point, they are released to find suitable substrate to become the sedentary scyphostomae (Mayer, 1910).