Kristian Fauchald fell in love with worms when he was 14 years old and in Norway, far above the Arctic Circle.

Volunteering after school in the museum in Tromso (pop. 13,000), Fauchald had already decided he was going to be a biologist when he grew up. One day he asked the curator of invertebrate zoology what might be a good subject for study.

"Why don't you do the polychaetes?" he recalls the man saying. "I have a huge collection and nobody who can identify them for us."

Fauchald took the advice to heart. By the time he left town at the end of high school, he'd worked his way through dozens of segmented marine worms resting on the bottom of jars of alcohol.

Now 64 and a curator of invertebrate zoology in his own right, he's still at it.

Fauchald inhabits the world of scientific research that exists invisibly behind the walls of Washington's great museums. His institution is the National Museum of Natural History. There, with several colleagues, he keeps and studies a collection of 2.5 million worms in 500,000 different "lots," representing about 3,000 species.

The worms are stored in glass jars filled with 70 percent ethyl alcohol. Thus housed, the animals shrink slightly and lose their color, but otherwise stay remarkably intact. Every five years, the preservative in every jar is topped up.

One of the two biggest worm collections in the world--the other is at the Natural History Museum in London--the Smithsonian's was begun in earnest 120 years ago by scientists with the U.S. Fish Commission. But it's not the inert and antique curiosity it appears to be when one first gazes on a thousand metal bookcases crammed with screw-top jars.

About 2,000 new lots come in each year, collected mostly from fresh- and saltwater habitats that are home to most of the world's worms. Hundreds also leave, to sojourn in the laboratories of biologists around the world. It's a lending library for worms.

There is something antique, however, in the work of Kristian Fauchald.

He comes out of "systematics," the venerable school of biology that categorizes plants and animals. That task is an essential step in reconstructing the history of life on Earth and in understanding the adaptive strategies that permit biological diversity. The goal is to construct family trees depicting species' relatedness. The problem--and to researchers like Fauchald, the delight--is that things keep changing.

"We probably have hundreds of thousands of species to describe," he says of worms. (Queried, he modestly admits he's described 200 new ones himself.) "It's sort of like insects, but not quite as bad. Our job is not quite as overwhelming as an entomologists.' They probably have millions left to describe."

The operative term here is "describe." Physical structure is the vocabulary of systematics. People like Fauchald describe, and in most cases sketch, individual animals.

In the past, attribution of a specimen to species, genus and all the other taxonomic categories depended on the observer's thoroughness, judgment and familiarity with like (or somewhat like) organisms. All those are still important, but in recent years, old-style systematics has moved toward the new, computer-driven art of cladistics, more commonly the realm of molecular geneticists.

Molecular geneticists deduce the relatedness of organisms by sampling their genes and comparing the DNA sequences. Computer programs sort the organisms into groups, or clades, based on the similarity of the DNA strands. Researchers like Fauchald now do something very similar. They describe an organism, noting the presence or absence of innumerable physical features. The descriptions are fed into a computer, which compares them and proposes various family trees. The scientist then judges which is the likeliest genealogy.

"We are rearranging the world repeatedly to our satisfaction. At least momentary satisfaction. Then we have to do it again," Fauchald says.

This means that the worms come out of their jars for study more than one might think. Often, they're even partially dissected.

It's a rich and complicated, though small, corner of scholarship. Only about 200 people in the world specialize in polychaetes, the class of segmented worms--mostly from the ocean--that is Fauchald's specialty.

Fauchald travels about three months of the year--with snorkel and mask--seeking new specimens. He has a preference for the tropics.

"I am not fond of cold water," he says. "I did my duty in it when I was in Europe. I do not see why I shouldn't study interesting problems in warm water."

Players

Kristian Fauchald

Title: Chairman, Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution.

Age: 64

Education: University of Bergen; doctorate, University of Southern California.

Family: Lives with a domestic partner, Leonard P. Hirsch, who is a political economist at the Smithsonian and president of the Gay, Lesbian and Bisexual Employees of the Federal Government.

Previous jobs: Associate professor of biology, University of Southern California.

Special interests: Classical music, travel.

On why he does research in the tropics: "I am not fond of cold water. . . . I do not see why I shouldn't study interesting problems in warm water."