Cassiopea (upside-down jellyfish) is a genus of true jellyfish in the family Cassiopeidae. 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 photosynthetic dinoflagellates and therefore must lie upside-down in areas with sufficient light. 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.

Species

According to the World Register of Marine Species, the genus includes 12 species:

  • Cassiopea andromeda <small>(Forsskål, 1775)—Indo-Pacific, introduced in the Mediterranean</small>
  • Cassiopea culionensis <small>Light, 1914</small>
  • Cassiopea depressa <small> Haeckel, 1880—Western Indian Ocean off the African coast</small>
  • Cassiopea frondosa <small>(Pallas, 1774)—Western Atlantic, Caribbean Sea</small>
  • Cassiopea maremetens <small>Gershwin, Zeidler & Davie, 2010—Western Pacific Ocean, off the Australian Coast</small>
  • Cassiopea mayeri <small>Gamero-Mora, Collins, Boco, Geson III & Morandini, 2022</small>
  • Cassiopea medusa <small>Light, 1914—Pacific Ocean, Philippines and Palau Region</small>
  • Cassiopea mertensi <small>Brandt, 1838—Pacific Ocean Southern Micronesia</small>
  • Cassiopea ndrosia <small>Agassiz & Mayer, 1899—Pacific Ocean, Australia and Fiji</small>
  • Cassiopea ornata <small>Haeckel, 1880—Pacific Ocean, Palau, Philippines, Okinawa</small>
  • Cassiopea vanderhorsti <small>Stiasny, 1924</small>
  • Cassiopea xamachana <small>Bigelow, 1892—Caribbean Sea and the Northern Atlantic Area of the West indies</small>

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.