The smooth periwinkle, Littorina obtusata, was probably the most common snail in the intertidal zone before the common periwinkle, Littoringa littorea, was introduced from Europe. Our native species has developed several color morphs, likely an adaptational response to predation. Interestingly, the snails can't change color, and they don't appear to know what color they should maintain as a background to help camoflauge them from predation. Depending on the color of the background, some snails are safely camoflauged while others stand-out and are preyed upon. Nevertheless, by having several colors within the gene pool the species is successful and can survive throughout the different colored backgrounds of the lower intertidal zone.
On our first transect, five different students in our M&M class each found one smooth periwinkle, but forgot to tell the data recorder. The students were: Josh, Camille, Hoory, Amanda, and Ryan. The snails that they found were four different colors (two yellow, and one each of red, brown, and green) and were found on several backgrouds of different colors (two were found on Irish moss, and one each were found on knotted wrack, kelp and sea lettuce). From the following statements, help us determine the color of the periwinkle found by each student and upon what algae it was found so we may correct the data sheets before Petr finds out.
1. The snail that was green was found on the red algae, Irish moss.
2. Neither of the two snails that were found on Irish moss were yellow, and neither were they found by boys.
3. Amanda found a yellow snail but she is sure it was not on kelp.
4. Neither Josh nor Camille found yellow or green snails.
*Modified from: Willis, N.D. 1995. Tricky Logic Puzzles Sterling, NY. 96 pp.