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Sizing up zooplankton

Zooplankton come in a wide range of sizes, for comparison, here’s a Calanus copepod next to a krill. The krill or euphausiid is about one and one-half
centimeter long while copepods are usually three millimeters or just over from tip to
tail. The other two tiny copepods —one at the bottom and one at left— are
Pseudocalanus, which are only one millimeter long. Imagine an animal as big as a
60-foot bowhead whale can support itself on animals this teeny. But then, these
animals are pulling off a similar trick, eating microzooplankton 1/1000th their
size.
(Photo by Chris Linder, Woods Hole Oceanographic Institution)