Some eat fish tongues, others castrate their hosts. Are parasitic isopods the world's most disgusting aquatic creatures, asks Matt Clarke.
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The photograph above isn't a fake. This is a real creature known as Bathynomus giganteus, or the Giant isopod. Although it looks like a fantasy creature from a sci-fi film, this is actually a genuine organism that lives in the depths of the Atlantic and Pacific Oceans and was first discovered off the Gulf of Mexico in 1879. It's believed to be a scavenger that feeds upon dead whales and squid in the pitch black darkness of the bathypelagic zone, some 2140m/7020ft below the water surface.
It's quite grotesque to look at, but it's not nearly as disgusting as some of its other cousins in the Order Isopoda. Take the Tongue-eating louse, Cymothoa exigua, for example.
This member of the isopod family Cymothoidae is a parasite and attaches itself to the tongue of fishes, usually snappers, holds on with its claws and drinks blood from the artery that lies within the tongue. Eventually, the tongue withers away due to the reduced blood supply, but the parasite remains, turning into a replacement tongue that the fish can use as normal - in return for a share of each meal consumed.
These tongue-eating parasites appear to be getting more common. One of the parasites, Cymothoa exigua, was found on the mouth of a snapper purchased from a fishmonger in London last year. And, in the same week, scientists reported a huge outbreak of Cymothoa indica on a catfish farm in India, where they attacked a cage full of Mystus gulio.
We've also noticed a number of images from our dive photography contributors recently which feature the parasites tucked away in the mouths of the fish. And, our catfish contributor Ian Fuller found this similarly disgusting cymothoid parasite in the gut of a dead Corydoras. Probably a Riggia, reckons Pete Liptrot.
Now, it seems, they're going for the genitals. At least, sort of. In a round about kind of way.
A team of scientists from Brazil has studied parasitism by another cymothoid parasite called Riggia paranensis, which apparently exhibits something known as "parasitic castration". See this news story for more details.
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