IT'S HARD TO BELIEVE long-running Richmond Latin dance band Bio Ritmo started life as a dreadlocked drum circle. Stylish and innovative, the group has morphed into a suave, sexy rhythmic beast.

Singer Rei Alvarez says the beast was born when its core of percussionists went searching for new rhythms and settled on the sounds of Tito Puente and Ray Barretto — leaders of New York's Puerto Rican jazz and salsa scenes of the '60s and '70s.

"I remember putting on an old Fania record from the era and saying, 'That's it! That's the sound we want to play!'" he says.

Alvarez and his fellow rhythmatists were all old hands at rock and reggae, but found switching to salsa took some work. And Alvarez had to adapt: "I got asked to sing back-up vocals, which I thought I would never do, since I was always happy to hide behind the drums," Alvarez says. Now Bio Ritmo's frontman, Alvarez just lets his cool charisma do most of the work.

After signing up some spicy horn players, the band enlisted its sole female member and secret weapon, keyboard player Marlysse Rose Simmons — a controversial move, initially.

"We were warned about a woman coming to fill in," says Alvarez, speaking of chauvinistic concerns that Simmons wouldn't be strong enough to keep up or fit in. "Salsa is very macho. … Salsa is music made by men for women." While noting the importance of Celia Cruz, Alvarez says, "it's a gentleman's world."

But Alvarez says Simmons was a knockout player and a much-needed catalyst after Bio Ritmo's many permutations over the years. And, in a sign the band's time has come, the group recorded its latest album, "Bionico," with Jon Fausty, Fania Records' engineer in the '70s.

"Working with Jon was like salsa boot camp," says Alvarez. "We came out of it with a lot of confidence in ourselves. Before, we were a band trying to play salsa. Now, we're a salsa band playing whatever it is we feel like."

» Iota, 2832 Wilson Blvd., Arlington; Thu., Oct. 31, 9:30 p.m., $12; 703-522-8340. (Clarendon)

Written by Johnathan Rickman for Express