Specie Pelagia noctiluca is a member of Scyphozoa jellyfish which is in completely adapted to a pelagic mode of life. Whereas most Scyphozoan jellyfish have a complex life cycle with both medusa stage and polyp stage, P. noctiluca has adapted in such a way that the polyp stage is absent, thus direct development exists, from planula to ephyra. Bell shaped body is compound of exumrella and subumbrella. The edge of its bell shaped body has been diveded on marginal lobes and in between are eight long tentacles. In the center od subumbrella is a so called manubrium on which we can notice mouth. Mouth lead to a digestive cavity divided with four barrier. Body of this Scyphomedusa is covered all over with nematocytes whose function is defense, pray, capture and killing of „pray“. It is spotted on the places od high salinity, poor with nutrients mostly until 150 meters of depth. Prefers warm waters of the Mediterranean sea, where can cause health problems on swimmers. Carbon dioxide rising these days and pH getting lower or „acidification“ is highly correlated with this Scyphomedusa dynamic and distribution.