Identifying obscure and bizarre objects is all in a day’s work for staff in the Queensland Museum Discovery Centre! Today Colleen Foelz joins us to share her mystery object of the month for August.

What am I?

At 30 centimetres in length, am I:

An over-sized model of a small land animal?

A life-size giant of the ocean?

Or a replica of a prehistoric sea creature?

Here’s a little hint

I’m a crustacean; a group that also includes animals such as crabs, prawns, barnacles, microscopic copepods and terrestrial slaters. I have 14 legs. I use the first three pairs to get food into my four-jawed mouth, and the next four pairs as walking claws. My abdomen has specialised segments called pleopods which are used for swimming.

The correct answer is “a life-sized giant of the ocean”. Meet the deep-sea isopod called Bathynomus giganteus (bathy = deep, nomus = home). It has been recorded at depths of 1800m but probably goes even deeper than that!

These isopods are an example of ‘deep-sea gigantism’, where deep-sea animals are larger than their shallower water counterparts. Other creatures with deep-sea giants include squids, spider crabs, sea spiders and jellyfish.

There are more than 20 species of deep-sea isopod. They are divided into two groups:  the giants, which mature when they reach a length of 15cm; and the supergiants, which can grow to 50cm, or maybe more! As the name suggests, B. giganteus is the largest known species, making it a true supergiant!

Giant isopods inhabit the sea floor where they scavenge on dead fish, squid, sponges, other crustaceans, and debris that falls to the bottom of the ocean. Deep-sea scavengers don’t have a regular food supply, and commonly have to wait for months or years between meals. A large carcass (such as a dead whale) falling to the sea floor provides such an abundance of food that giant isopods have been observed gorging themselves to the point that they can barely move.

Female isopods produce numerous eggs; those of B. giganteus are the largest of all, with a diameter of about 1cm. Young giant isopods develop in a type of pouch called a marsupium. They emerge looking much like miniatures of the adult.

Worldwide there are over 10,000 species of isopod found in the sea, in freshwater and brackish water, and on land. They are scavengers, detritus feeders, parasites and predators.

You may be familiar with the land-based isopods known as slaters, pillbugs, rollie pollies or woodlice. They look very similar to the giant isopod—except they are MUCH smaller. They have an important role in maintaining soil health. Just like their diminutive landlubbing cousins, giant isopods can curl up in a defensive posture to protect their underside.

Ask an expert

Visit the Discovery Centre to see this Mystery of the Month this August.  Do you have an interesting question or mystery object? Our helpful and knowledgeable staff can answer your questions through our Ask an Expert inquiry service.