Pelagia noctiluca

Pelagia noctiluca is a jellyfish in the family Pelagiidae and the only currently recognized species in its genus. It is typically known in English as the mauve stinger, but other common names are purple-striped jelly (causing potential confusion with Chrysaora colorata), purple stinger, purple people eater, purple jellyfish, luminous jellyfish and night-light jellyfish. In Latin, pelagia means 'of the sea', nocti stands for night and luca means light; thus, Pelagia noctiluca can be described as a marine organism with the ability to glow in the dark (bioluminescence). It is found worldwide in tropical and warm temperate seas, although it is suspected that records outside the North Atlantic region, which includes the Mediterranean and Gulf of Mexico, represent closely related but currently unrecognized species. A fairly small and variably coloured species, both its tentacles and (unusual among jellyfish) bell are covered in stinging cells. Stinging incidents are common, painful and the symptoms may continue for a considerable time after the encounter, but they are generally not dangerous. When large numbers of this oceanic species are washed ashore, the local economy can be affected because tourists avoid the beaches and fishers are stung while trying to retrieve their nets, which can be clogged by the jellyfish. Additionally, swarms of Pelagia noctiluca have been recorded wiping out entire fish farms. Because of this, it has become one of the most studied jellyfish species. 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. Some of the locations are California (rare), Hawaii (rare), and all around Australia (common). However, it is suspected that Pelagia noctiluca—as currently defined—is a species complex with records outside the North Atlantic region involving other closely related species that presently are unrecognized or undescribed. Even North Atlantic and South Atlantic populations show significant genetic differences. 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. This also means that the species sometimes appears in waters outside its normal temperature preference, with records as far north as the Shetland Islands and the Norwegian deep. It generally occurs at water temperatures between 10 and 27 °C (50–81 °F), but below 11 °C (52 °F) it stops pulsating. It mostly ranges from the surface to a depth of 150 m (490 ft), but has been recorded to 1,400 m (4,600 ft). Pelagia noctiluca partakes in the diel vertical migration, occurring near the surface at night and deeper during the day. 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). 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. However cnidaria have evolved cnidae, cells which serve for a variety of functions that include prey capture, defense, locomotion and attachment. When fully formed cnidae are called cnidocytes. When stimulated the cnidae secrete nematocyst toxins that are biological poisons. These organisms have a well-developed manubrium, a proboscis-like structure bearing the mouth and four long oral arms. Also the mesoglea, or jelly, is relatively thickened and well developed in this species. Sense organs, known as rhopalia in the scyphomedusae, are located around the umbrella margin in notches and alternate between tentacles. Cnidae are present in the epidermis and gastrodermis of the umbrella, as well as on the tentacles.