I raided the library for books about fish and other ocean animals so the students could use the images for reference. One of the students told me that dolphins are a type of whale and I didn't believe him until I looked it up! I couldn't believe that after all the books I read when I was little and random trivia I know, I had never heard that before! I required the students to have at least one animal and something in the foreground- either sand, rocks, seaweed, reef, etc. Some students also included treasure chests, sunken ships, and scuba divers.
I was surprised at my 3rd grade student's Beatles reference and he was equally surprised that I got it!