The Mark of Athena (The Heroes of Olympus, #3)

by Rick Riordan

Aphros nodded, a glint of pride in his eyes. “We have trained all the famous mer-heroes! Name a mer-hero, and we have trained him or her!” “Oh, sure,” Leo said. “Like…um, the Little Mermaid?” Aphros frowned. “Who? No! Like Triton, Glaucus, Weissmuller, and Bill!”