But what they did not expect was a three-foot-long alligator.

It seems that Mr. Volpe, 32, and Ms. Volpe, 25, were keeping the reptile as a pet, the police said.

Neighbors of the Volpes, who live at 2246 West Sixth Street in Bensonhurst, said that while they saw the couple arrested, they had never seen the animal.

"I had no idea there was an alligator in there," Eric Pampano, 19, said.

Not surprising, since it is unlikely it would have been taken out for walks in the neighborhood.

Still, it is hardly the first time that the authorities have stumbled upon an exotic animal in a person's home that might better belong in a zoo or in the wild.

In September, a menagerie of exotic animals — including six snakes (one boa constrictor and five pythons), two bearded dragons, two alligators, a gecko, a scorpion and a tarantula — was removed from an apartment in Crown Heights, Brooklyn.

At the Volpes' home, the police suspected criminal behavior and found two loaded handguns, a loaded shotgun and marijuana, according to the authorities.

The couple were arrested and the officers called animal control to remove the alligator.

In addition to gun and drug offenses, the Volpes were charged with harboring a prohibited animal. It is illegal to keep a wild animal as a pet in New York City without special permission from wildlife authorities.

Paul Fox, 20, a student who lives nearby, said that he watched as the police stormed the house on Monday and was not surprised that there were drug-related arrests.

"The kids that hang out there are not a good crowd," Mr. Fox said. "But an alligator? Why would you want an alligator in your basement?"

Christopher Maag contributed reporting.