Isopod Got Your Tongue? Naturally Tongueless Animals

Isopod Got Your Tongue? Naturally Tongueless Animals
Some animals are naturally tongueless, but certain unlucky fish lose their tongues to parasites.

“If the host’s tongue is unoccupied…”

Isopods of the family Cymathoidae look like oversized fleas and inhabit shallow marine, brackish or fresh subtropical waters—and some of the fish that live there. These tiny invertebrates float along in the ocean mimicking prey items. When swallowed by a fish, the isopod first attaches itself to the fish’s gills. It then latches onto and eats the fish’s tongue—giving these isopods the nickname of “tongue biters”—and takes up residence as a replacement tongue for the fish.

All tongue biters enter the fish’s gills as males, but that can change. “The majority of tongue-biting isopods are protandrous hermaphrodites,” says Denham Parkerof Rhodes University in South Africa, via email. They start out as male but are able to transform into females.

“If the host’s tongue is unoccupied, the male isopod moves from the gills and attaches to the tongue,” Parker says. Once attached, it transforms into a female, which is much larger, and consumes and replaces the tongue, all of which probably happens simultaneously. It then waits for another male to occupy the fish’s gills.

They will stay there and breed, with the female releasing fertilized eggs into the water.

The fish survive the parasitism, but it may take a toll on them, Parker reported in 2013. He collected largespot pompano from a bay in South Africa and found that being parasitized with Cymothoa borbonica isopods affected the fish’s growth, probably because the tongue biters make eating and breathing more difficult. The fish, however, usually outlive the parasites.

Parker says there’s no evidence that eating an infected fish will cause any harm to humans.

Taste sensations

Other animals naturally have no tongues, such as sea stars, sea urchins and other echinoderms, as well as crustaceans, says Chris Mah via email. Mah is a marine invertebrate zoologist at the Smithsonian National Museum of Natural History and has discovered numerous species of sea stars.

Sea stars are omnivorous, Mah points out on his Echinoblog, and feed in different ways, including swallowing prey items whole or by pushing their stomach out through the mouth and using it to take in prey, no tongue required.

Insects, too, are tongueless, Philip Koehler, an entomologist at the University of Florida, writes via email. But they still manage to get along fine without one.

Butterflies and flies taste with their feet. And fruit flies have taste receptors all over their bodies, including on their wings and ovipositors, the opening through which they lay eggs.