I was expecting the manta ray. I wasn't expecting what came on top: Black shards of blubbery flesh that shined like wet clam shells.

The sea is full of wonderful and frightening surprises, and this is definitely one of them. Aleta de atun ("tuna fin") is a specialty of Ciudad Obregon, Sonora, where food truck owner Braulio Lopez found it. He says the meat comes from a specific fin on the bottom of the fish.

At his truck Baja Mar - Mariscos y Cahuamanta, they slow boil the fin along with a slab of sting ray meat for several hours. The two go onto shop's Taco Super Baja Mar along with whole shrimp and squishy little octopus disks and tentacles.

The creation is kind of a Tour de Gulf of California: a mountain of sea life on double-stacked corn tortillas with cabbage, onions and tomatoes. The manta ray on the bottom was soft and shredded in red sauce, almost like a heavier tuna fish without any gaminess. It was the base for the spunkier ingredients like the octopus. (Sadly, I think they forgot to put on the shrimp that day.)

The tuna fin? Well I guess I'll be honest. It was really sticky and gummy and smelled like something you'd find in a tidepool. Even the the guy working the line said it wasn't his favorite. But apparently, "A lot of people like it!"

Weird fact: The Sonoran specialty cahuamanta — which usually contains a mixture of manta ray, shrimp and sometimes tuna fin — used to be prepared with turtle meat until our favorite reptilian friend was put on the endangered species list.    

Locations: I caught up with Baja Mar on the northeast corner of Oracle Road and Miracle Mile. But there's a second truck on northeast corner of East Drexel Road and South Nogales Highway. NEWS! Lopez says that in a couple of weeks they plan to open a third Baja Mar on 22nd Street and Wilmot outside the La Mexicana Mercado y Carniceria. 

Phone: 520-940-7784

Hours: 8 a.m. to 4 p.m. Sundays through Thursdays, 8 a.m. to 5 p.m. Fridays and Saturdays

Payment: cash only

Contact Andi Berlin at aberlin@tucson.com. On Twitter: @AndiBerlin

You can find the Star's digital food writer Andi Berlin at a taqueria near you, taking tiny bites and furiously scribbling into an old notepad.