Speaker 1: "Yeah, we found mostly those tiny shellfish that have strong hard shells that act as protection."
Speaker 2: " But not FROM other organisms that might eat them, predators?"
Speaker 2 is finishing the thought for Speaker one. The complete sentence is implied. "Yeah, we found mostly those tiny shellfish that have strong hard shells that act as protection, but not from other organisms that might eat them, like predators."
In other words, the strong hard shells protect them, but they're not strong enough to protect them from predators.