Just the shells are amazing, each as pretty as its name: queen conch, triton's trumpet, shinbone tibia, sea butterfly, Atlantic deer cowrie, wavy clio, Reeve's turban, purple bubble-raft snail.

You'll come across the skull of Dunkleosteus, jaw bones sharpened like teeth. This is a creature that doesn't appear safe to approach even though it's been dead for more than 350 million years. A few feet away gapes the maw of Carcharodon, the giant great whale shark, a term that doesn't seem so redundant when you see it in person.

Five years in the making and open to the public since late September, the Sant Ocean Hall, named after philanthropists Victoria and Roger Sant, may never become as popular as the dinosaur hall (what can compete with that?), but it is a vast improvement over the old ocean hall, demolished a full decade ago.

The museum needed its ocean back. Museum Director Cristian Samper had an overriding directive as he supervised this, the first major project in his five-year tenure: ''I said this couldn't be a hall just about fish.''

It's not an aquarium. In fact, other than one small coral-and-fish aquarium, there's hardly any water - just the evocation of water through a blue-green color scheme. What there's lots of is video, including a high-definition film, shot underwater, projected on eight large screens around the top of the hall and offering the visitor something of an illusion of being immersed in the sea.

And there are lots of specimens. ''This is a specimen-rich hall,'' Samper says. There are 674 species on exhibit, including a giant squid so gray and nasty that it could sink a ship on looks alone. When the Spanish offered this rare giant squid to America, the U.S Navy and Air Force handled the transfer and dubbed the mission ''Operation Calamari.''

Looming over the hall is a fake whale precisely modeled after a real whale that, at this very moment, is swimming around and spouting off in the real Atlantic Ocean. Her name is Phoenix. She's 21 years old. She's a North Atlantic right whale. There are fewer than 400 of her kind left, thanks to two centuries of aggressive whaling, ship collisions and other environmental insults. The fake Phoenix is true to the real Phoenix all the way down to the odd encrustations on her lip and the scars on her tail from the time she got tangled in a fishing line.