FaunaHub

Giant Isopod (genus Bathynomus)

Marine invertebrateCrustaceanDeep sea

Giant isopod (Bathynomus) — a large deep-sea crustacean.

Giant isopod (Bathynomus).

Image: Eric Kilby from Somerville, MA, USA, CC BY-SA 2.0, via Wikimedia Commons.

Overview

Giant isopods (genus Bathynomus) are large crustaceans of the deep sea — distant marine relatives of the woodlice (pill bugs) found in gardens. Encased in a segmented, armoured exoskeleton with many legs and large compound eyes, they are a striking example of “deep-sea gigantism,” in which some deep-water animals grow far larger than their shallow-water relatives.

They live on the cold, dark seafloor and are best known as patient scavengers that can endure long stretches between meals.

Note: deep-sea animals are difficult to study, and many details of giant isopod biology are still being researched. Figures and ranges should be treated as general and verified against authoritative marine sources.

Habitat & Range

Giant isopods live on the floor of deep oceans, generally in cold waters well below the sunlit zone, across the Atlantic, Pacific, and Indian Oceans depending on the species. They favour soft, muddy bottoms where food sinks from the waters above.

Diet

Giant isopods are mainly scavengers, feeding on the carcasses of fish, whales, squid, and other animals that fall to the seabed (“marine snow” and larger food falls). Because food is scarce in the deep, they can gorge when they find a carcass and then survive remarkably long periods without eating.

Behavior

Life in the deep sea is slow and energy-conserving. Giant isopods move along the bottom searching for food and can roll up for protection, much like their land relatives. Their large eyes help detect the faint light and movement of the deep, and they are thought to be long-lived and slow-growing, as is typical of deep-sea animals.

Human Interaction & Conservation

Giant isopods are rarely encountered by people except through deep-sea trawling, research expeditions, and aquarium displays, where their unusual appearance makes them popular. They are not currently a major conservation focus, but deep-sea habitats overall are increasingly affected by human activity. Consult authoritative marine sources for current information.

More photos of the giant isopod

Giant isopod Bathynomus giganteus, dorsal view.

Giant isopod (Bathynomus giganteus).

Image: NOAA, Public domain, via Wikimedia Commons.

Frequently Asked Questions — Giant Isopod

Are giant isopods related to woodlice?
Yes — distantly. Giant isopods are crustaceans in the same broad group (order Isopoda) as the woodlice or pill bugs found on land. The deep-sea giants are simply far larger marine members of that group, an example of deep-sea gigantism.
How can giant isopods survive so long without food?
The deep sea offers little food, so giant isopods are adapted to feast when a carcass arrives and then live on those reserves with a very slow metabolism. Individuals in captivity have been recorded going extraordinarily long periods between meals.
What do giant isopods eat?
Mostly carrion. They scavenge the bodies of fish, whales, squid, and other animals that sink to the seafloor, and they will also take some slow-moving live prey. This scavenging role helps recycle nutrients in the deep sea.
How deep do giant isopods live?
They are bottom-dwellers of the deep ocean, generally found well below the sunlit surface waters, with the exact depth varying by species. Because the deep sea is hard to study, precise ranges should be checked against current marine references.

Sources and further reading

Authoritative wildlife references used for general educational context. Conservation status should always be verified against current IUCN Red List data. External links open in a new tab.