Mariachi music and jellyfish go hand in tentacle, so to speak.

You probably thought moon jellyfish and mariachi music had nothing in common. But this weekend both arrive in the South Bay, offering residents a chance to visit with the sea creatures and celebrate Latin sound.

On Saturday, the Cabrillo Marine Museum in San Pedro unveils its long-awaited exhibit “Open Ocean: The Vast Frontier,” starring rarely seen ocean life. In Wilmington, meanwhile, the 11th annual Wilmington Fiesta begins--a two-day festival featuring music by well-known mariachi bands, a menudo cook-off and activities for children.

The “Open Ocean” exhibit, which cost $75,000 and was three years in the making, provides an unusual glimpse of deep-sea life along the Pacific coast. The display is one of few in the world to include a colony of living moon jellies--fragile, translucent jellyfish that are shaped somewhat like a flattened umbrella and live hundreds of feet below the ocean’s surface, said Mike Schaadt, exhibit director.

The jellyfish are easily observed in a stretch planktonkreisel , a thin, flat specially designed aquarium with rounded corners that Schaadt likens to an ant farm. Unlike other jellyfish, the delicate moon jellies have a “wimpy sting” that poses no threat to humans, Schaadt said.

Through models, colorful graphics and preserved specimens, the exhibit also introduces visitors to deep underwater residents such as the flap-jack devilfish, the triple-wart sea devil and the vampire squid. Although these animals are common off the coast of California, scientists and scuba divers are usually the only people to see them, Schaadt said.

“The exhibit enables people to understand that life on earth is never-ending in variety,” Schaadt said. “Just when you think a llama is unusual, along comes a vampire squid.”

The 11th annual Wilmington Fiesta offers lively, if more familiar, fare this weekend.

Bandstand highlights will include a performance Saturday at 4 p.m. by Los Camperos, the mariachi group best known for its concert and recording work with pop star Linda Ronstadt and appearances Sunday by Los Galleros and Sol de Mexico, two mariachi bands that packed the Hollywood Bowl last month. Latin jazz, reggae and oldies music fill out the music roster.

“It’s a great way to spend all or part of a summer weekend,” said John Mendez, co-chairman of the event.

Awaiting young visitors are carnival helicopter and swing rides, clowns, face painting and, from 1 to 4 p.m., arts and crafts activities.

Cooks can cash in on their culinary talents by competing in the Menudo Cook Off on Saturday beginning at 10 a.m. The top three winners will be awarded prizes ranging from $200 to $500. Interested contestants should call (213) 835-1751.

Free eye exams, hearing and blood pressure tests will be offered by the Lion’s Club Eyemobile on Sunday from noon to 4 p.m.

Proceeds from the event go to the Wilmington Teen Center, youth baseball programs and other community activities.

What: “Open Ocean: The Vast Frontier,” a new exhibit at Cabrillo Marine Museum

When: Begins Saturday, 10 a.m. to 5 p.m.

Where: Cabrillo Marine Museum, 3720 Stephen White Drive, San Pedro

Admission: Free

Information: (310) 548-7562

What: 11th annual Wilmington Fiesta

When: Saturday and Sunday, noon to 8 p.m.

Where: Banning Park, 400 E. Pacific Coast Highway, Wilmington

Admission: $3 before 2 p.m.; $5 after 2 p.m.

Information: (213) 835-1751