Speedy Crustaceans

By HENRY FOUNTAIN The tiny shrimplike crustaceans known as copepods are the nitro-burning dragsters of the planktonic world. They are only about an eighth of an inch long, but some varieties can go from zero to 200 (body lengths per second, that is) in the space of a few milliseconds when confronted with danger.

Researchers from the University of Hawaii at Manoa have suggested one reason why some of these creatures, which constitute one of the major sources of protein in the ocean, exhibit such speed. Borrowing a trick from the vertebrates, some copepods have myelin-like sheaths on their nerve cells.

Myelin acts much like the insulation on a piece of wire, enabling electrical impulses to travel faster along nerve cells. Such speed improvement is thought to be especially valuable in large vertebrates, where nerve impulses must travel over long distances. But myelin and similar substances are being found in an increasing number of invertebrates where, because of their small size, speed would not necessarily be considered crucial.

The Hawaiian researchers, reporting in the journal Nature, found myelin-like sheaths in 11 species of copepods. And they found that those with the sheaths responded significantly faster to stimuli than those without the sheaths.

From the April 20, 1999 Science Times