From Earth Science Picture Of The Day; July 27, 2014:
Photographers: John Stetson, Katy Stetson (bottom photo); Summary Author: John Stetson
Don’t stare at the above photo — you might turn to stone. Yes, this creature is a medusa (Hydrozoa). But it happens to be smaller than 100 microns, less than the width of a human hair. This medusa is a type of bioluminescent jellyfish named after the Greek mythological character with snakes coming out of her head. It was captured in a plankton tow at the Southern Maine Community College; Bethany Brown, Tammy St. John and Crystal Cooper provided the water samples containing the medusa from nearby Casco Bay.
From an evolutionary standpoint, the medusa and its kin are quite interesting creatures. Jellyfish are the oldest multi-organism animals. They’re also the first swimmers. Note, plankton don’t really swim. Rather they just move with the wind, changes in water density and the tide.
The bottom photo shows a porpita (blue button), a marine animal related to jellyfish that wander the ocean in colonies. The porpita is much larger than the medusa. The medusa is microscopic; the porpita … macro. Photos taken on July 7, 2014.