Bob Dubinskas wears a 24-inch gold chain around his neck. At the end of the chain is a shell, painted with gold and white stripes. Seymour lives inside the shell. "It's so much fun," says Dubinskas, a 16-year-old sophomore at Rockford (Mich.) High School. "Seymour hangs from my sweater and crawls all over me when he's happy."

Seymour is a hermit tree crab the size of a quarter, one of about a dozen that have turned up on necklaces sported by students at the 1,400-student school. The kids got the idea from James Allemon, a local gift-shop owner who began selling the Caribbean crabs on chains, at $6.95 each last fall.

"I was the first kid in my school to do it," reports Monica Leeuwenburg, 16. "One day my crab came out of its shell during my first-period English class. We were in groups, discussing something boring, like paragraphs. One girl screamed, and then I had to go to the principal. Wow! It was great."

Not everybody shares Monica's enthusiasm. "These crabs can't stand drafts, and it doesn't take much to kill them," says Karen Fountain, a manager at the Grand Rapids Humane Society. "Dangling from a chain is unnatural. It's like a dog living in a doghouse at a 45-degree angle." Ann Sullivan, a cruelty investigator at the society, concurs: "It's outrageous. I worry about a child who wears something like this."

Allemon says that crab jewelry isn't cruel. "I'm pro-crab," he says. "The chains go through the shells, not the crabs. You have to use common sense with this, as with any pet. For instance, you wouldn't take a parakeet out in 25-degree weather; it's the same with crabs."

Leeuwenburg, whose crab is named Future, says: "My crab gets the best treatment. I don't wear him 24 hours, and I treat him like a pet, not jewelry." Future dines out on peanut butter sandwiches and crab food and resides in a terrarium when he's not being used as a fashion accessory.

Of course, there's more than one good reason for students to be kind to their crabs. Come June, what young man wouldn't be proud to appear at the prom wearing a white sport coat and a pink crustacean?