This might look like the result of some wild nuclear accident, but in fact this worm is perfectly healthy. It just happens to glow bright green when exposed to certain wavelengths of light.
A team of researchers from the Scripps Institution of Oceanography in La Jolla, California has discovered that it's a humble splash of vitamin B—riboflavin to be precise—which causes the parchment tube worm to glow.
Interestingly, if you prod and poke the beast, it spits out puffs of mucus that glow bright blue light, too—but it's not clear yet what creates that particular hue. That piece of research is, apparently, next on the list. [Physiological and Biochemical Zoology via New Scientist]