Jellyfish diameter; the tentacles and mouth parts usually extend beyond this bell dimension. The smallest jellyfish are the peculiar creeping jellyfish in the genera "Staurocladia" and "Eleutheria", which have bell disks from to a few millimeters in diameter, with short tentacles that extend out beyond this, which these jellyfish use to move across the surface of seaweed or the bottoms of rocky pools. Many of these tiny creeping jellyfish cannot be seen in the field without a hand lens or microscope; they can reproduce asexually by fission (splitting in half). Other very small jellyfish, which have bells about one millimeter, are
Cyanea (jellyfish) Cyanea (jellyfish) Cyanea is a cosmopolitan genus of stinging jellyfish, primarily found in northern waters of the Atlantic and Pacific Oceans. The same genus name has been given to a genus of plants of the Hawaiian lobelioids, an example of a "parahomonym" (same name, different kingdom). The taxonomy of "Cyanea" species is not fully agreed upon. Some zoologists have suggested that all species within the genus should be treated as one. However, in the North Sea at least, the lion's mane jellyfish and the blue jellyfish appear as distinct species. "Cyanea" may be a species complex of recently diverged species.