You've probably never encountered a giant isopod unless you spent some time fishing in the depths of the ocean and accidentally caught one in the tangles of your fishing net.
Maybe you've seen one in captivity in one of the few aquariums that house it. Regardless, you might be fascinated to know that there are tons of these huge, insect-like creatures living in the darkest depths of the sea. And yet, they remain a mystery to us humans.
“There's a lot we don't really know about these guys,” says Ruth Carmichael, senior marine scientist at the Dauphin Island Sea Lab and professor of marine and environmental sciences at the University of South Alabama. But what scientists do know is that “they have a really important job [debris recycling] that we need animals to do in the deep ocean.” More on that in a minute.
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- Isopod versus giant isopod
- How giant is a giant isopod?
- What are giant isopods like?
- What do giant isopods eat?
Isopod versus giant isopod
Giant isopods are essentially giant versions of isopods. What is an isopod, you ask? Isopods are a type of arthropod, explains Carmichael. Arthropods are invertebrate animals such as lobsters and shrimp, but also insects and spiders. The common denominator is that they all have tough and flexible exoskeletons.
Isopods are further reduced taxonomically into an order of crustaceans called Isopoda , which consists of several flattened, segmented animals. There are more than 10,000 species of isopods worldwide that include marine, freshwater and terrestrial species. Perhaps the best-known isopod is the chubby bug, also known as the stink bug or potato bug.
Not all isopods are alike, but they have some characteristics in common, such as:
- two pairs of antennas
- compound eyes (eyes with multiple lenses)
- four sets of jaws
- a body made up of seven segments, each with its own pair of legs
For the most part, marine isopods are small, “the size of a fingernail or up to 2 inches long,” and are most common in marshes and estuaries, says Carmichael. Giant isopods are marine animals that live in the depths of the sea – from 152 to 2,133 meters deep – mainly in the western Atlantic, western Pacific and Indian oceans.
They are also much, much larger than all the other isopods.
How giant is a giant isopod?
There are actually two size classes of giant isopods, explains Carmichael – giant isopods and supergiant isopods. Regular giant isopods are about 8 to 13 centimeters long. “Think of a chart,” she says. Supergiant isopods are even larger, up to 51 centimeters long. “So if you think about a professional basketball player’s shoe – like Michael Jordan’s size 13 – that’s the small end of a supergiant isopod. They can be about one and a half times that size,” she says.
What makes giant isopods and supergiant isopods so gigantic is the same type of phenomenon seen in other deep-sea marine creatures, like the giant squid. In zoology, the term is called “deep-sea gigantism.” It is the tendency of animals that live in deep waters to grow much larger than their relatives that live in shallow waters.
Why this occurs has baffled scientists, but one theory is that gigantism may help these creatures withstand the extreme pressure of their underwater environment. Another idea is that gigantism is the result of adaptations to scarce food resources at the bottom of the sea. It is also believed that decreasing temperature results in increased cell size and increased lifespan, which can lead to increased maximum growth and larger size.
What are giant isopods like?
Giant isopods look surprisingly similar to the tiny chubby ones that live on land, except their exoskeleton is brown or light lavender. And like their chubby cousins, giant isopods can curl up into a ball and use their tough outer layer as a shield.
Similar to chubby ones, the giant isopod's body is made up of seven overlapping segments. In giant isopods, these segments are called pleonites. The first is fused to the head and projects over the animal's large, widely spaced eyes like a helmet. The eyes have more than 4,000 individual facets that reflect light, making them appear to glow.
The six remaining segments of the giant isopod form the abdomen, and each isopod has seven pairs of pereopods, or legs. The first pair of pereopods are designed to help push food into the animal's four sets of jaws, which then cut and tear the prey. The other legs, called swimming legs, are used for swimming.
In front of the head is a fan-shaped tail, called a uropod, and fluttering swimmers, called pleopods. They work together to propel the giant isopod through the water and also to help with breathing.
Giant isopods also have two sets of antennae sprouting from their heads – a short pair and a long pair that extends about half the length of the body. This helps guide the animals through the dark, murky depths of the ocean.
What do giant isopods eat?
“As far as we know, they are primarily scavengers,” says Carmichael, vacuuming up debris that has fallen to the ocean floor, including live and dead fish, crabs, shrimp, squid, sponges and whale carcasses. “They play an important role in recycling nutrients and elements.”
Relying on deep-sea food sources can be a feast or famine situation, but that's not a problem for giant isopods. When food supplies are plentiful, these creatures don't mind gorging themselves, although this tends to make it difficult for them to get around. And in times when supplies are scarce, giant isopods can also adapt. In protected environments, such as aquariums, they survive up to four years without food.
Now that's disgusting
Think the giant isopod is scary? Check out one of the best-known isopods, the tongue-eating parasitic louse. “It actually sucks the blood out of the fish’s tongue and causes the tongue to die and fall off,” says Carmichael. “This little guy sits in the place of the fish’s tongue and if you look inside the fish’s mouth you will see a segmented, wormy thing sticking out.”
