Blue jellyfish

A bioluminescent predatory cnidarian native to the Glisalian Ocean of Glisal II, the blue jellyfish floats passively on the current with its almost invisible tendrils outstretched in order to reflexively sting, paralyze and digest anything unfortunate enough to tangle with its many arms. Iridescent markings curve along its domed shape which are sometimes mistaken for some sort of skull, giving rise to a variety of eerie nicknames and stories to keep unsupervised children out of the water.