sea snail vs seashell

sea snail

noun
  • Any saltwater snail; a marine gastropod mollusk with a shell (contrasted with sea slug). 

seashell

noun
  • The empty shell of a marine mollusk. 

  • A very light pink colour, like that of some seashells. 

adj
  • Of a very light pink colour, like that of some seashell. 

How often have the words sea snail and seashell occurred in a corpus of books? (source: Google Ngram Viewer )