Now That’s An Isopod (Bathynomus giganteus)

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The Giant Marine Isopod (Bathynomus giganteus) is currently the largest known isopod in the world.  Isopods are crustaceans, related to shrimp, crabs, lobsters, prawns, amphipods (side-swimmers or “scuds”), etc.  They are also related to “pillbugs” or the “roly poly” we find in our basements and gardens.  Most isopods are small.  In fact, it is relatively uncommon to see one larger than an inch or two in length, including both terrestrial and aquatic species.  There are about nine species in the genus (Bathynomus) inhabiting the sea floors of both the Atlantic and Pacific Oceans.  As I understand it, they can be locally abundant where they occur.  

The strange appearance of these invertebrates has captured people’s attention.  While science has known about Bathynomus giganteus for an excess of a hundred years, the internet has helped to boost awareness of them in the general public.  For example, a fairly recent story related a situation where a submarine returned to the surface with one of these isopods attached to it.  Apparently one of the deck hands took some shots, posted them on the web, and asked what it was.  The images became an over night internet sensation and thrust Bathynomus giganteus into the limelight.  Subsequent stories have kept the creature in the collective conscious of Americans who, by and large, are either horrified or fascinated, perhaps a little of both.

Having been fascinated by deep water marine life, I always hoped I’d get to see one of these creatures live.  My opportunity came to pass not out at sea but at the Shedd Aquarium in Chicago.  I can not complement the Shedd enough for their spectacular exhibits and their attempts to display uncommonly seen animals.  They have done a magnificent job.  I’d like to thank them for allowing me to photograph one of their Bathynomus giganteus specimens.  Not sure if I would have ever been at the right place and time to see one hauled up on a ship’s deck from the depths.  If you do happen to visit the Shedd Aquarium, make sure to take a moment and see these spectacular invertebrates!

Bathynomus giganteus lives on the deep ocean sea floors of the Gulf of Mexico and the Caribbean.

Bathynomus giganteus was described in 1879 by Alphonse Milne-Edwards.

This specimen is not a particularly large individual. They can attain lengths of roughly 30 inches (~76cm). Why deep sea isopods get so large is an interesting question. Deep sea gigantism (also known as “abyssal gigantism”) comes into play. This is a phenomenon whereby relatively small life forms in shallow waters have deep sea relatives that are larger than “normal.” Some biologists have hypothesized that the cold temperatures of bathypelagic habitats produce larger cell sizes, resulting in larger life forms. Another argument suggests that because the habitat where these animals are living is so cold that most things are long lived and simply have a greater period of time to get larger. Another more recent argument is that the depths provide an advantage for body temperature control. The stable temperatures of the deep sea are involved, which undoubtedly affect body temperature regulation, and in turn may affect the dynamics of surface area to mass ratios. Regardless of the cause behind the phenomenon, there are some great examples of deep sea gigantism including the Japanese Spider Crab and the Colossal and Giant Squids.

Bathynomus giganteus is believed to mainly be a scavenger on the ocean floor, eating the carcasses that make it to the depths. Some have suggested that they may also prey upon other small and slow moving invertebrates.

The species can be found as shallow as ~550 feet depth (~180m) down to over 7,000 feet depth (~2,330m).

The alien appearance of the Giant Marine Isopod.

Bathynomus giganteus has compound eyes.

There are two pairs of antennae in Bathynomus giganteus.

Females develop a brood pouch and keep their developing young in the pouch. Juveniles emerge as miniatures of the adults and are called mancae. There is no larval stage.