pearlfish

[purl-fish]
noun, plural pearl·fish·es, (especially collectively) pearl·fish.
  1. any of several small fishes of the family Carapidae, living within pearl oysters, sea cucumbers, starfishes, etc.

Origin of pearlfish

First recorded in 1585–95; pearl1 + fish
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018