seashell vs shellfish

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. 

shellfish

noun
  • A fisheries and colloquial term for an aquatic invertebrate having an inner or outer shell, such as a mollusc or crustacean, especially when edible. 

  • A culinary and nutritional term for several groups of non-piscine, non-tetrapod, aquatic animals that are used as a food source. The term often exclusively refers to edible aquatic crustaceans, bivalve mollusks and cephalopod mollusks; but sometimes echinoderms may be included as well. 

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