cassiopea

Cassiopea is a genus of scyphozoan jellyfish very commonly found in shallow mangrove swamps, mudflats, and turtle grass flats in Florida and various other similar environments around the world, where it lives usually upside-down on the bottom. Where found, there may be numerous individuals with varying shades of white, blue, green and brown. They have a mild sting since they are primarily photosynthetic, but sensitive individuals may have a stronger reaction. The stinging cells are excreted in a mucus; swimming over these jellies (especially using swim fins) may cause transparent, essentially invisible, sheets of this mucus to be lifted up into the water column, where they are then encountered by unsuspecting swimmers. The stings, appearing in the form of a red rash-like skin irritation, are notorious for being extraordinarily itchy.

The Cassiopea jellyfish (one common species is Cassiopea andromeda) belongs to the Order Rhizostomeae and mostly lives in sandy areas and seagrass beds. The Cassiopea jellyfish is also called "Upside Down Jellyfish", because it lies on its back, so that the bell touches the ground. In this position it resembles a sea anemone. Sometimes this jellyfish is picked up by a crab (Dorippe frascone) and carried on its back. The crab uses the jellyfish to defend itself against possible predators.

Rhizostomae or Rhizostomeae is an order of jellyfish. Species of this order have neither tentacles nor other structures at the bell's edges. Instead, they have eight highly-branched oral arms, along which there are suctorial minimouth orifices. (This is in contrast to other scyphozoans, which have four of these arms.) These oral arms become fused as they approach the central part of the jellyfish. The mouth of the animal is also subdivided into minute pores that are linked to coelenteron.

Cnidaria ( /naɪˈdɛəriə/ with a silent c) is a phylum containing over 10,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance, sandwiched between two layers of epithelium that are mostly one cell thick. They have two basic body forms: swimming medusae and sessile polyps, both of which are radially symmetrical with mouths surrounded by tentacles that bear cnidocytes. Both forms have a single orifice and body cavity that are used for digestion and respiration. Many cnidarian species produce colonies that are single organisms composed of medusa-like or polyp-like zooids, or both. Cnidarians' activities are coordinated by a decentralized nerve net and simple receptors. Several free-swimming Cubozoa and Scyphozoa possess balance-sensing statocysts, and some have simple eyes. Not all cnidarians reproduce sexually. Many have complex lifecycles with asexual polyp stages and sexual medusae, but some omit either the polyp or the medusa stage.