Step into the alien world of giant isopods, where prehistoric charm meets deep-sea mystique. These creatures are the rockstars of the abyss. They’re oversized, armored, and utterly mesmerizing. Let’s find out some interesting facts about this species!
Class: Malacostraca
Order: Isopoda
Family: Cirolanidae
Giant isopods are older than dinosaurs
The giant isopod is an ancient creature dating back over 160 million years. It even showed up even before dinosaurs like the tyrannosaurus rex. These enigmatic beings have thrived in the Earth’s oceans for an unimaginable duration.
Do you know which species are they related to? Woodlouse. Despite their big discrepancy in size and distant connection to these tiny dwellers, giant isopods share a fascinating link. Both species share a defensive mechanism—curling up into a ball to protect themselves when threatened, safeguarding their soft underside with a robust exoskeleton shell.
They are the biggest isopods
The giant isopod is the biggest isopod among thousands of isopod species and is a fascinating creature that has been known since its discovery in 1879.
This species is a type of crustacean, a distant cousin of crabs. It boasts a notable size of up to 20 inches (51 cm), showcasing deep-sea gigantism, where organisms evolve to much larger sizes compared to their terrestrial relatives (like the pillbug). However, not all giant isopods are that big. Their adults usually have a size of about 3.1 and 5.9 inches (8 and 15 cm) in length.
Similar to other crustaceans, this sea creature has jointed legs and a thick external covering known as an exoskeleton, comprising interlocking segments. Its body comprises three segments: the head, thorax, and abdomen, fused for strength and flexibility. The abdomen consists of five curved pieces with branches or flaps for movement and respiration.
The species has 14 jointed legs, arranged in seven pairs, serve various functions, including holding and moving food to the mouth and swimming. One of the most outstanding features of this isopod is its distinguishing large, fixed compound eyes spaced far apart. These eyes, comprising over 4,000 individual facets, appear to glow due to a reflective layer called the tapetum.
These creatures navigate their surroundings using large eyes and two pairs of antennae – one short and one long – located at the front of their body. These spindly sensors can reach nearly half the length of their bodies.
Giant marine isopods come in shades of brown or pale lilac, presenting a uniform appearance across most species. However, you can differentiate them through the distinctive shapes of the spines on their tails and other structural nuances.
Habitat
The giant isopod is a deep-sea dweller. They live in the cold waters of the Pacific, Atlantic, and Indian oceans, particularly in the benthic region. The majority of giant isopod specimens are found off the coast of eastern Australia, with four Atlantic species ranging from the state of Georgia to the Gulf of Mexico in the Caribbean.
Adapted to the deep sea, they can endure the darkness of depths exceeding 1600 feet (500m), where sunlight is scarce, amounting to less than one millionth of what is found at the ocean’s surface. These bottom dwellers are capable of surviving at various depths, with some species living as deep as 2500 meters or 8200 feet below the water’s surface. Remarkably, one species has even been discovered thriving in relatively shallow waters of 980 feet. Their preferred habitat includes mud or clay seafloor.
It’s said that the harsh conditions of the deep ocean, characterized by extreme pressure, colder temperatures, and limited food availability, have led to the development in their body size.
They can go for years without eating
Giant isopods are skilled scavengers, eating what they can find. Their scavenging behavior is driven by their harsh habitat where food and sunlight are scarce.
Living at the bottom of the ocean, these deep-sea isopods patiently await a buffet of leftovers from above. Their diet often includes marine worms, crab bits, whale falls, marine snow, fishheads, and animal carcasses.
However, marine snow is not always available. That’s why these huge isopods have developed an exceptional adaption: they slow down their metabolism and energy to survive. The species can go for long periods of time (about 4 – 5 years) without eating. But when food is abundant, these non-picky eaters gorge themselves to the point that they cannot move.
Despite being primarily scavengers, there is evidence that giant deep-sea isopods can also be carnivores, feeding on live animals like slow-moving sea cucumbers, shrimp, sponges, or fish.
To find prey in the dark, they rely mainly on chemoreception and possibly mechanoreception, a sensory receptor that responds to mechanical pressure or distortion. They use their 4 sets of jaws designed for cutting, tearing, and eating prey.
Thanks to their remote location in the deep sea, giant isopods don’t have many predators. Besides, their natural armor, including a thick outer shell, deters potential threats. In some countries, these species are eaten as food by humans.
Behavior
Giant isopods spend most of their time on the seafloor waiting for food. They often burrow into sediment for shelter, adopting a semi-hibernation state due to the uncertainty of future meals, conserving energy for essential functions like breathing and moving.
These sea isopods can also swim freely and glide through the water. Their large antennae assist them in navigating the dark seafloor and locating prey. The small antennae serve primarily for chemical sensing, while their larger counterparts are employed in the realm of physical sensation.
For locomotion, these isopods employ a fan-like tail and small, fluttery limbs, enhancing both movement and respiration. Their legs feature hooked claws for stability on the rugged ocean floor.
These adaptations collectively contribute to their unique existence in the challenging deep-sea environment.
While the giant isopod may seem intimidating, it’s neither venomous nor poisonous.
Reproduction
The mating season of giant isopods takes place in seasons of abundance like spring and winter. During this time, females develop a specialized brood pouch composed of overlapping plates above their stomachs—an internal marvel known as a marsupium.
Within this protective chamber, females carefully lay approximately 20 to 30 eggs, distinguished by their impressive 13 mm diameter, making them some of the largest among marine invertebrate eggs.
What’s even more intriguing is the maternal dedication exhibited during the brooding period. During this time, females won’t eat anything, they retreat and bury themselves in sediment. This dual-purpose tactic not only conserves energy but also protects their precious eggs from predators.
The juveniles hatch from the eggs, exhibiting full development and closely resembling adults, but smaller in size. These young measure approximately 6 cm (3.4 in) in length, with the absence of only the final pair of pereopods distinguishing them from mature individuals.
As young isopods progress in age, they undergo frequent molting to attain larger sizes; however, this molting activity decreases in frequency as they reach maturity. Unlike many other marine organisms, giant isopods bypass a larval stage in their life cycle. The lifespan of the giant isopods is said to be more than 4 years.
Conservation Status
While the giant isopods may not show up on the IUCN Red List, they remain vulnerable to the repercussions of human actions.
The vital role of brooding females is jeopardized as deep-sea trawlers inadvertently entangle them, contributing to a concerning decline in their populations. Adding to the environmental challenges, these deep-sea dwellers are now grappling with the ingestion of plastic debris. So, even in the remote expanses of their habitat, these isopods are still impacted by human threats.
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