This tentacle belongs to a blue button (Porpita porpita), an animal that looks like a jellyfish but isn’t. While it has a central “float” with streaming tentacles like typical jellyfish, the blue button is a colony of many small hydroid animals. Some of the individual animals (zooids) make up the float, while others make up the tentacles. Despite differences, there is one major similarity: the tentacles have stinging nematocysts in those white tips, so do not touch! This image, taken at 50x zoom, was an Image of Distinction in the 2010 Nikon Small World photomicrography competition.