entozoon

entozoon (plural entozoons or entozoa)

1. (obsolete) Any of various microscopic parasitic worms previously classified together under the grouping Entozoa.
   • 1903, Herbert Spencer, Essays on Education and Kindred Subjects‎:

     The discovery that a disorder known as "the staggers," of which many thousands of sheep have died annually, is caused by an entozoon which presses on the brain, and that if the creature is extracted through the softened place in the skull which marks its position, the sheep usually recovers, is another debt which agriculture owes to biology.