Cassiopea (upside-down jellyfish) is a genus of true jellyfish in the family Cassiopeidae.[3] They are found in warmer coastal regions around the world, including shallow mangrove swamps, mudflats, canals, and turtle grass flats in Florida, the Caribbean and Micronesia. The medusa usually lives upside-down on the sea floor in shallow areas, which has earned them their common name. They have a symbiotic relationship with photosyntheticdinoflagellates and therefore, must lie upside-down in areas with sufficient light.[4] Where found, there may be numerous individuals with varying shades of white, blue, green and brown. They have distinctive methods of reproduction and prey capture, and are unusual in that they appear to sleep despite lacking a brain.[4] They also have toxic proteins in their mucus.[5]
Cassiopea xamachanaBigelow, 1892—Caribbean Sea and the Northern Atlantic Area of the West indies
Reproduction
Cassiopea individuals are gonochoristic, being either strictly male or female. Like other jellyfish, they have a gastrovascular cavity with only one opening. This is where fertilization primarily occurs. After fertilization, the embryos are expelled and attach to the oral disc, where they remain for 48 hours. By the 96-hour mark, they elongate and become polyps, resembling the adult form.[4]
Cassiopea Species Distribution MapCassiopea sp. in seaweed
Sleep state
Certain species of Cassiopea have been observed to enter a sleep state displaying three primary characteristics. These are quiescence, also known as inactivity or dormancy, delayed responsiveness to stimuli (or sensory depression), and homeostatic regulation, allowing them to remain stable despite changes in the outside environment. They are the first animals lacking a central nervous system to have been observed sleeping.[4] When Cassiopea are provoked, they release mucus that contains toxic proteins.[5]
Swimming
The method of swimming in Cassiopea is unique to jellyfish. They create their own propulsive water currents when changing direction by contracting a mushroom-shaped part of their body called the bell. This contraction creates whirlpools that are broken up as they flow between the oral armsproducing a constant flow of water towards the animal and an upward flow above it.[4]
Nutritional requirements
Upside-down jellyfish gain few nutrients from the waters around them, and their method feeding is not well known. They are known for a symbiotic relationship with algae, allowing them to photosynthesize as a whole organism, producing glycerol and glucose.[4]
Feeding habits
Cassiopeia species feed by pulsating to move the water around them and pull in prey under their bell and grasp it with their oral arms. They hold the prey in place using small oral vesicles attached to the arms, fragmenting it and passing it into secondary mouths, where it is digested by ciliated cells. They are opportunistic predators, feeding on crustaceans, nematodes, and eggs.[5]
123456Ohdera Aki H.; Abrams Michael J.; Ames Cheryl L.; Baker David M.; Suescún-Bolívar Luis P.; Collins Allen G.; Freeman Christopher J.; Gamero-Mora Edgar; Goulet Tamar L.; Hofmann Dietrich K.; Jaimes-Becerra Adrian; Long Paul F.; Marques Antonio C.; Miller Laura A.; Mydlarz Laura D.; Morandini Andre C.; Newkirk Casandra R.; Putri Sastia P.; Samson Julia E.; Stampar Sérgio N.; Steinworth Bailey; Templeman Michelle; Thomé Patricia E.; Vlok Marli; Woodley Cheryl M.; Wong Jane C.Y.; Martindale Mark Q.; Fitt William K.; Medina Mónica (2018). "Upside-Down but Headed in the Right Direction: Review of the Highly Versatile Cassiopea xamachana System". Frontiers in Ecology and Evolution. 6: 35. doi:10.3389/fevo.2018.00035. hdl:11449/176281.
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