crustacean vs rock lobster

crustacean

noun
  • Any arthropod of the subphylum Crustacea, including lobsters, crabs, shrimp, barnacles and woodlice. 

rock lobster

noun
  • A crustacean of the family Palinuridae. 

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