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7 of the Most Revolting Parasites Found in the Ocean

If you can stomach it, these parasites will make you appreciate what some species will do to survive underwater.


Warning: This list, which features some of the most disgusting parasites in the ocean, is not for the faint of heart. However, if you can stomach it, these parasites will make you appreciate what some species will do to survive underwater.

1. The tongue-eating louse

Source: Wikimedia Commons/Marco Vinci

This parasitic crustacean does exactly what its name suggests. It enters a fish through the gills and latches onto the tongue, which causes the tongue to atrophy. The tongue-biter then replaces the tongue with its own body.

2. Rhizocephalan barnacles

Source: Wikimedia Commons/Hans Hillewaert

This parasite is an unusual species of barnacle that invades crabs. It injects cells of itself into the crustacean, establishing tendrils or roots all over the animal's insides and steals much of its nutrients. The details are magnificently graphic, and you can read a more thorough explanation of how this gross parasite operates here.

3. Glugea stephani

Source: Wikimedia Commons/Hans Hillewaert

This fungal parasite, typically found in various flatfish species, goes straight for the gut—literally. It's a type of microsporidian parasite, which infects the cells of their hosts and invades the organs and tissues; Glugea stephani is known to attack the intestines in particular. Pictured here is a dab with a large growth caused by the parasitic infection.

4. Schistocephalus solidus

Source: Deep Sea News

The Schistocephalus solidus is a truly disgusting-looking hermaphroditic tapeworm parasite species that infects three different animals. Copepods, or small crustaceans, are the first victims, inadvertently consuming the parasitic larvae swimming in the same water.

A fish then consumes the copepod, and that's where things get ugly. The worm grows to gargantuan sizes and in some cases can grow to weigh even more than the fish it's infected. The infection begins to affect the fish's brain chemistry, behavior and immune responses, likely contributing to its unfortunate fate: ingestion by a bird, the worm's final host.

Within 48 hours after the parasite has attacked the bird's intestines, it reaches reproductive maturity and produces eggs. It dies soon afterward, but the eggs are passed with the bird's feces and hatch in the water, where the whole cycle starts all over again.

5. Trematoda

Source: Wikimedia Commons

Trematoda are class of parasitic flatworms that can be found in the intestines of fish and mollusks, such as sea snails. Pictured here is the Botulus microporus, a species that lives in the intestines of lancetfish. These guys typically go through two hosts in their lifetime.

6. Cod worm

Source: Wikimedia Commons/Hans Hillewaert

This blood-sucking parasite is a marine copepod that lives on the surface of its hosts. It infects two victims in its lifetime: first a flounder or lumpsucker, and finally cod. If you're a big fan of seafood, you might wonder if there's any way one of these lovely creatures could show up in your freshly bought fish one day—and the answer is yes.

In fact, it's not uncommon for consumers to discover a wriggly (still moving!) worm in store-bought cod. Food Republic shared one man's account of this unappetizing discovery here.

7. Lernaeenicus sprattae

Source: Wikimedia Commons/Hans Hillewaert

Also called the eye maggot of sprat, these parasites live on sprat fish and carry two egg sacs (these are the blue appendages in the above photo).

Now, who's hungry?

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