The Mystery at the Base of One of Biology’s Strangest Relationships

For starters, you need to know that a fish tongue is not like a human tongue. Our tongues are flexible, muscular, and magnificently mobile; they help us speak, suck, swallow, whistle, lick, taste, and tease our friends. Fish tongues—properly called basihyals—don’t do a lot of those things. They are, in their most basic form, just flat stubs of bone, perhaps topped with a scant pad of soft tissue, that protrude from the base of the mouth. They help fish shuttle food down and push water through gills, and don’t do a ton else.

But like a human tongue, the fish tongue doesoffer a highly accessible strip of blood-rich meat, parked in an oft-opened hole in the head—excellent bait for a parasite. Some eons ago, a few called isopods happened upon this revelation. They became teeny terrors known as , and several have since gained a reputation for nomming away at lingual appendages until little to none of