pinnothere

noun1

1. •
   (no longer used) A small crab of the genus Pinnotheres, which live symbiotically in the shells of certain molluscs.

   • The shell-fish called a Nacre, liveth even so with the Pinnotere, which is a little creature like unto a Crabfish, and as his porter or usher waits upon him, attending the opening of the Nacre[…]. — 1603