I first encountered the existence of giant deep sea isopods a few years back, when I was convinced that they were Photoshopped.  Someone somewhere posted a picture of three giant isopods seemingly attacking a bag of Doritos.  What were these things?  They set the internet afire, starting with this Something Awful article.

I still don't really know what the deal is with that Doritos picture.  

At any rate, isopods are a group of crustaceans loosely related to shrimp and crabs.  You may be familiar with one of the land-living isopods, the wood louse (known also as the "roly poly" or "pill bug").  Most isopods are relatively small, but some isopods grow very large indeed.  About the size of a cantaloupe, according to one of the more recent finds.

A contractor working for a benthic survey company posted some pictures of a SUPER giant isopod to Reddit.  This isopod must be a record breaker; although most other giant isopods have been about a foot long, this fellow was 2.5 feet long!  The isopod apparently attached itself to the survey company's ROV, and rode it all the way to the surface.  (It appears not to have survived the trip.)

Although most giant isopods live far down in the depths, there are a few which inhabit shallower waters.  These are caught and served as seafood in Thailand.  I assume these shallow water dwellers are also the ones which are occasionally displayed in aquariums.  I poked around a little, and learned that the Newport Aquarium just outside Cincinnati has some giant isopods in their "Dangerous & Deadly" display.  According to one visitor's report, they are not very lively.  I'd still like to see some, though!

Isopods are an important link in the ecology of the deep ocean.  As scavengers, they help redistribute the wealth, so to speak.  The cold temperatures and high pressures of the deep ocean make it difficult for the usual decay processes (led by bacteria) to take place.  By eating fallen corpses and pooping out the digested remains, isopods take those nutrients that would otherwise be locked up in the corpse and release them back into the ocean at large.

Apparently the deeper the water, the fewer giant isopods, but the bigger they are.  This makes me wonder how far that goes.  Is it possible that at the base of the Marianas Trench, a single giant isopod the size of a couch is cruising around looking for fallen whales?  Probably not, but it's fun to think about.

One thing the giant isopod has in common with the giant squid (Archeteuthis) is a phenomenon dubbed "deep sea gigantism."    This is, according to Wikipedia, "the tendency for species of deep-sea-dwelling animals to display a larger size than their shallow-water counterparts."  Thus the correlation between the depth of the water and the size of the giant isopod.  

There are a few theories on deep sea gigantism, including advantages for less loss of body heat and as a response to the greater pressure of the benthic environment.  But what it really comes down to is, we have no idea!  As a general rule, we know less about the deep ocean than we do about the depths of the universe.  Anything could be down there, really.

And it could be a fan of Doritos.

Image copyright Reddit user Gwynzer