In an natatory episode of The New York Times series ScienceTake, host James Gorman shares fascinating footage of the wonderfully shape shifting garden eels, who pop out of their hiding places in the seafloor to catch food that’s floating by. When the current is low, the eels bend to reach the plankton in the water while staying anchored to their holes. When the current is moving fast, the anchored eels fashion their bodies into the shape of a question mark to stand firm as their food rushes by. The eels just as easily slip back down into their little hidey-holes when danger is nearby (or if they just want to rest without worrying.)
The eels seem to be unique among fish. They are capable of swimming free, which they do to change burrows. But mostly, they live sessile lives, anchored in their narrow burrows even when they emerge to feed, like tethered snakes striking at zooplankton too small to see.