Periphylla periphylla, the helmet jellyfish.
Despite this jellyfish’s ability to produce phosphorescence, other forms of light are toxic to it. For this reason, helmet jellies usually only move up in the water column at night in search of their planktonic food. Unlike most other cnidarians, P. periphylla does not have an anchored larval stage; rather, it remains pelagic throughout its entire lifecycle.
I was skeptical when I first read the ‘other forms of light are toxic’ line, but whoa, their own pigments that give them their coloration can really turn lethal when exposed to light of certain intensity (phototoxicity? photodegradation? so it was a bit like inverse melanin?)
Fascinating stuff. Read more here
No matter how long the slinky is, the bottom of the slinky will stay still (hover) until the top reaches it. Even if the slinky is over 1000 feet long.
tension in the slinky between the top and the bottom form an equilibrium with gravity, meaning no change in position is caused as the forces are equal.