Blue Christmas
Photograph courtesy John Huisman, Murdoch University

At the slightest touch, these "Christmas trees" temporarily disappear down a hole faster than you can say "Grinch." It's a defense mechanism of the Christmas tree worm, most of which resides in a tunnel it carves into live coral.

Photographed off Australia's Lizard Island by a Census of Marine Life expedition, the two blue trees are actually a single worm's "crowns"—each spiral is a series of tentacles used in breathing and in passive feeding on tiny, floating foodstuffs.