Pelagia noctiluca

, Australia 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. There are reports from most other tropical or warm temperate seas around the world, including both the Pacific and Indian Oceans, with its apparent southern limit being 42nd parallel south. Hawaii (rare), and all around Australia (common). A comprehensive taxonomic review is necessary to resolve the situation. In 2014, a second species in the genus Pelagia was described from the Mediterranean, but two years later it was moved to its own genus as Mawia benovici. The swimming ability of Pelagia noctiluca is limited and as a result large swarms (also known as blooms) of this oceanic species are occasionally carried by the wind or current to inshore areas, sometimes ending up stranded on beaches. Local populations fluctuate greatly and the species may go virtually unrecorded in a region for years, only to suddenly reappear in huge swarms. On occasion, a swarm may cover tens of square kilometers, include millions of Pelagia noctiluca, and reach densities of more than 500 individuals per m3 (14 per ft3). == Description ==

in the Mediterranean Pelagia noctiluca are fairly small jellyfish with adults having a bell diameter of . == Behavior ==

Life cycle and reproduction in the Mediterranean Sea 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. Ephyrae stages reside in the upper mixed layer above the shallow thermocline. The bottom-living polyp stage of most other jellyfish species is in between the planula and ephyra stages. P. noctiluca rely on favorable trophic conditions to spawn, so when their criteria is not met, the medusae will stop reproducing immediately and lose weight when presented with an inadequate amount of food. Large swarms of adults at the ocean surface in certain times of the year possibly are spawning aggregations. 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. Cannibalism where adults consume young of their own species is also common in P. noctiluca. Feeding reactions were studied by Bozler (1926), where a piece of food was given to the marginal tentacle, the tentacle contracted quickly. There was a slow contraction of the coronal muscle which brought the tentacle nearer to the mouth. The food was grasped by the lip of one of the oral arm and transported slowly along until it reached the stomach. They were found to feed on the salp Thalia democratica; however, they are found mainly to feed by taking food particle by the amoeboid process of the endoderm cells, thus being suspension feeders. == Sting ==

Pelagia noctiluca is considered the most important stinging jellyfish in the Mediterranean Sea. The sting causes pain that typically lasts 1–2 weeks, local redness, swelling and a rash, but it is generally not dangerous and there are no known fatalities. On occasion, symptoms may be more general and include dizziness, vomiting and diarrhea. Sudden recurrent skin eruptions may occur years later. Rarely, the sting can cause a serious allergic reaction and leave scars or hyperpigmented marks on the skin that can remain for years after the encounter. Peculiarly, there is a record of a seven-arm octopus "borrowing" the stinging capability of a P. noctiluca. The open-sea octopus grabbed and positioned the jellyfish in such a way that it provided a defense. The sting of P. noctiluca can possibly be relieved with the use of Hydroxyacetophenone and Symsitive® since they are nematocyst inhibitor compounds, meaning they inhibit the discharge of cnidocysts. == References ==