Buzz
Crustaceans are well-known creatures: arthropods that reign over the oceans just as their insect cousins dominate the land. However, the crabs, lobsters, and shrimp we recognize are only a small glimpse into the immense variety and diversity of this group. Crustaceans inhabit nearly every aquatic habitat on Earth, from the icy Arctic waters to scorching toxic springs, encompassing a wide range of predators, scavengers, herbivores, and parasites.
10. Gribbles
Though it might seem unusual for a sea creature to feast on trees, enough driftwood makes its way into the ocean for certain marine organisms to rely on it as a primary food source. Isopods belonging to the Limnoriidae family, better known as “gribbles,” are a prime example, having adapted to exclusively consume submerged wood. These tiny sea termites, once capable of wreaking havoc on wooden vessels, are comparable in their destructive potential to the notorious “shipworms.”
Gribbles have been receiving increased attention recently. The enzyme they produce during feeding is highly efficient at breaking down wood into simple sugars—a process that could potentially be harnessed to create a sustainable source of renewable biofuel if we manage to replicate it.
9. Pea Crabs
Though humans may use the term “crabs” to describe some parasites, the only true crabs that engage in parasitism belong to the Pinnotheridae family. Small, soft-bodied, and fragile, these crabs live within the body cavities of clams, oysters, sea squirts, sea cucumbers, and various other marine organisms, where they feed on the food ingested by their host.
Pea crabs are edible and are sometimes unintentionally steamed and served inside clams. On occasion, they are intentionally harvested and prepared as a dish of their own.
8. Skeleton Shrimp
The Caprellidae are minute marine predators commonly known as “skeleton shrimp” due to their slender, ghost-like appearance. With their curved legs, they firmly attach themselves to coral, sponges, seaweed, and other surfaces, then lie in wait for unsuspecting prey. Some species live up to the notorious reputation of mantis shrimp mating rituals, with females injecting males with venom and consuming them shortly after mating.
Skeleton shrimp are frequently introduced into new ecosystems through human activity, and their populations can grow dense enough to completely cover submerged surfaces like an army of living velcro. These population booms can even decimate larger fish populations, as the skeletal creatures outcompete them for plankton and easily prey on newly hatched fish fry.
7. Buoy Barnacles
Once classified as mollusks, it was Charles Darwin who first recognized that barnacles were actually crustaceans. They traded mobility for a stationary, plankton-eating existence. However, at least one species has evolved to regain some mobility: the buoy barnacle, the only barnacle capable of secreting its own spongy “float” when it cannot find another suitable surface to attach to. In this way, it drifts along the ocean currents like an exoskeletal version of the Man O’ War.
These tiny ocean wanderers sometimes gather in large groups, forming floating rafts that can also become home to other barnacle species.
6. Remipedes
With long, segmented bodies and numerous paddling limbs, remipedes resemble swimming centipedes. They also have a prominent set of “fangs,” which are thought to inject venom. Studying these elusive creatures is difficult, as they inhabit deep, underwater caverns and saltwater aquifers. Their global distribution indicates that they were once more widespread, but evolutionary pressures likely forced these once-common species into their dark retreats millions of years ago.
In recognition of their monstrous appearance, a newly discovered family of Remipedes has been named “Godzilliidae,” with subfamilies including Godzilliognomus, Godzillius, and Pleomothra.
5. Whale Lice
“Whale lice,” or cyamids, are the largest arthropods known to live their entire lives on a mammal's body. They attach to the wrinkles, scars, and barnacles on the surfaces of whales and porpoises. While their presence might seem unpleasant, these tiny creatures only consume dead skin and algae, causing no harm to their hosts. In fact, they are responsible for the distinctive feature of the Eubalaena genus of whales; the unique white patches found on these whales are created by thousands of pale lice clinging to the animal's skin.
Interestingly, Cyamids also belong to the same family as the Caprellidae, or “skeleton shrimp,” mentioned earlier, having evolved away from their carnivorous behavior to adapt to the bodies of whales.
4. Pistol Shrimp
The Alpheidae, or pistol shrimp, are renowned for their extraordinary biological weaponry. By snapping their oversized claw, they create a collapsing cavitation bubble capable of paralyzing or killing small fish with its intense shockwave of sound and pressure.
While their biological stun guns are certainly impressive, they aren’t the only thing that makes pistol shrimp unique. Certain species are the only crustaceans known to form eusocial colonies—similar to ants or termites—featuring specialized reproductive “queens” and non-reproductive worker castes. These shrimp live and feed entirely within sea sponges, keeping harmful parasites at bay. They’re the bees of the ocean, armed with supersonic stings and living in symbiotic hives.
3. A Parasite’s Parasites
The parasitic barnacle Sacculina has been discussed in Mytour articles before, but let’s revisit it before we dive into our next crustacean. Sacculina’s mature form barely resembles an animal—early texts even mistook it for a fungus. After shedding 90% of her body, the female grows into little more than a mass of tissue that spreads through the body of her crab host, which is castrated and tricked into raising the parasite’s offspring. If the host is male, Sacculina manipulates its hormones, making it think and behave like a mother.
Before performing this incredible transformation, Sacculina needs to find a mate. Once she’s fully grown, she forms a large, tissue-filled sac on the outside of the crab’s body, known as an externa. Tiny male larvae of her species enter this sac, fertilizing her from within for the rest of their lives.
Sadly, the Externa exposes Sacculina to more than just her own kind; Liriopsis pygmaea, a parasitic isopod, targets the external sacs of parasitic barnacles, making it a parasite on a parasite—what biologists call a “hyperparasite.”
Much like its host, the isopod loses most of its recognizable traits as it matures, transforming into nothing more than a white, fleshy pearl. And just as the barnacle castrates the crab, these spherical lice make the barnacle sterile as well.
2. Pram Bug
Pram bugs are deep-sea predators often compared to the movie “Alien,” due to their unnervingly elongated heads and their gruesome way of life. When it’s time to raise her young, the female hunts down a gelatinous filter-feeder (a distant relative of vertebrates) and carves it into a hollow tube. This mutilated carcass becomes a mobile nursery that she steers through the water using her many paddles, keeping her eggs oxygenated. She regularly drags prey into the tube, tearing it apart so her young can feast on it.
1. Anchor Worms
A variety of copepod crustacean families go by the name “anchor worm,” which should tip you off that we’re dealing with some truly peculiar creatures. When they mature, these parasites shed any trace of being arthropods. Instead, they molt into blind, limbless tubes of tissue. They can be found clinging to fish or even other invertebrates.
Some species of anchor worms are bloodsuckers. They extend “roots” into the host’s body and turn a vivid red. More disturbing varieties embed themselves in fish eyeballs, feeding on the vitreous jelly. A few strange species feature a mouth at the end of a flexible, trunk-like appendage, which they use to graze steadily on the host’s body, sticking to the same small area for their entire lifespan.
One of the most unsettling anchor worms is Trebius shiinoi, found inside the uterus of female angel sharks. In many instances, they even spread to the unborn pups of pregnant hosts.
