Mauve Stinger

Pelagia noctiluca are fairly small jellyfish with adults having a bell diameter of 3–12 cm (1.2–4.7 in). Their colour is variable, ranging from mauve, purple, pink, light brown to yellow. The body is radially symmetrical. There is only one body cavity known as the gastrovascular cavity. This is a primitive gut or digestive cavity with only one opening that is used for ingestion and excretion; there are four long oral arms with crenulated margins that are the primary feeding surface. Each P. noctiluca medusa has eight long tentacles that emerge from the umbrella margin. Being radially symmetrical it has no head and thus no centralized nervous system. The nervous system present is primitive, consisting of a simple net composed of naked and largely non-polar neurons. In addition P. noctiluca also lacks a gaseous exchange, excretory and circulatory system.

This jellyfish is best known from the North Atlantic region, ranging from 4th parallel north (just north of Equator) to the North Sea and Atlantic Canada, including the Mediterranean and Gulf of Mexico.

Pelagia noctiluca are opportunistic and have been recorded feeding on a wide range of small organisms like planktonic crustaceans (cladocerans, copepods, ostracods and crustacean larvae), mollusk larvae, larvaceans, hydromedusae, siphonophorans, arrow worms, fish eggs and fish larvae, as well as detritus suspended in the open water and microscopic phytoplankton. The phytoplankton can be consumed either directly or indirectly by eating herbivorous crustaceans with stomachs filled with it. The ability to eat phytoplankton is—as far as known—highly unusual among cnidarians. P. noctiluca will eat small warty comb jellies (Mnemiopsis leidyi), potentially helping to control this invasive species. Cannibalism where adults consume young of their own species is also common in P. noctiluca. The stomach contents of P. noctiluca also vary throughout the seasons.

Pelagia noctiluca is adapted to a pelagic, open-sea mode of life. Whereas most jellyfish, including the other species in the family Pelagiidae, have a life cycle with both the free-swimming stages (planula, ephyra and medusa) and a bottom-living polyp stage, P. noctiluca has adapted in such a way that the polyp stage is absent. P. noctiluca reproduces sexually with the male and female spawning respectively sperm and eggs into the sea during daylight hours. After 3 days, the fertilized egg develops into a planula; at this stage movement is only done by ciliary action. After a week, planulae develop into tiny ephyrae and a month later they develop into (male or female) medusae. There is little or no ephyra growth at temperatures below 10 °C (50 °F), and fewer survive below 8 °C (46 °F). Ephyrae stages reside in the upper mixed layer above the shallow thermocline.