What Do Sea Cockroaches Look Like? Their Characteristics and How They Differ from Cockroaches
Many people have surely also often seen, in coastal rocky reef areas, on man-made structures such as wave-dissipating blocks, or on the embankments of fishing harbors, crowds clinging to the rocks and darting at lightning speed across sheer vertical walls pounded by surging waves - masters of martial-arts lightness skill, roaming every kind of rugged extreme terrain along the coast. They are what we commonly call "sea cockroaches."
The word "cockroach" instinctively brings to mind damp ditches or greasy, messy kitchens, or even the little roaches that appear in the corners of toilets. This title of humanity's number-one enemy, so irritating, makes most people shrink back the moment they hear the name of the sea cockroach, and so they lose the chance to get to know this amazing creature.
This Cockroach Is Not That Cockroach
This special forces unit living on coastal rocks is not the same as the kitchen cockroach. Sea cockroaches are not insects. Taxonomically, although both belong to the phylum Arthropoda, sea cockroaches belong to the order Isopoda within the subclass Malacostraca. The order Isopoda is quite widely distributed, from woodlice under the leaf litter of forests to sea cockroaches by the sea, as well as deep-sea water lice, all belonging to the isopods.
The most commonly seen sea cockroach by the seaside in Taiwan, China has the formal Chinese name "Ligia exotica," scientific name Ligia exotica Roux, a species belonging to the family Ligiidae. Sea cockroaches have seven pairs of appendages, growing respectively on seven thoracic segments, unlike cockroaches, which belong to the insects and have three pairs of legs. On close observation, sea cockroaches and cockroaches differ greatly in structure and are not closely related by blood; it is purely because their appearance, way of moving, and speed are quite similar that they are commonly called sea cockroaches.
A sea cockroach climbing on a gravel beach, where seven pairs of pleopods can be seen.
Ligia exotica is widely distributed along the coasts of the Pacific and Indian Oceans and is the most common crustacean in the coastal zones of Taiwan, China. Their body length is about 2 to 4 cm, and their vertically flattened body shape can reduce the resistance of washing by waves.
These sea cockroaches like to inhabit the coastal intertidal zone, occasionally moving upstream into nearby freshwater areas near river mouths. They are commonly seen in groups crawling among the crevices of gravel or wave-dissipating blocks, moving swiftly, and when in danger they can crawl underwater to evade enemies.
The Most Important Recycler by the Sea
Sea cockroaches generally move around near the high tide line of the coast and most of the time do not enter the water, but when in danger they will temporarily crawl into seawater. Their flat bodies help them charge across the rocky reefs of the surging intertidal zone, weave through the surf zone, and hide in rock crevices, like a lightning force, coming and going through the waves, moving through gravel areas, reef areas, and man-made facilities such as harbor wharves, wooden piles, and fishing boats, even making their homes on boats or driftwood. Near coastal river mouths in wetlands and fish ponds, and even in the filter tanks and drainage ditches of aquariums in metropolitan areas, these ninja-like strange visitors can be found.
Therefore, sea cockroaches, with their lightness skill of gliding like a breeze and climbing rocks and walls, can move freely through treacherous surf zones and even climb up coastal cliffs, using their lightness skill to pick up various organic debris along the wrack line at the water's edge of the intertidal zone, such as fragments of algae, drift material, and algae on rocks. In addition, small organisms, animal carcasses, and bait discarded by anglers are all their feasts. They waste not a single bit of food and can be called an important recycler by the sea.
According to literature reports, the breeding season of sea cockroaches is in spring. They are dioecious and ovoviviparous organisms, so occasionally paired mature sea cockroaches can be seen mating on intertidal rocks, with the male clinging to the female's body. Even so, their movement speed is still astonishingly fast, without the slightest hindrance; their extreme athletic and balancing abilities are amazing.
Diverse Species Distribution, Displaying the Beauty of Nature
Besides those living in the intertidal zone, another group of isopod species has also been found in deep-sea environments, and parasitic species have been found in both marine and freshwater environments. In marine museums and aquariums in China and abroad, species inhabiting the deep sea from the large isopod family Cirolanidae have also been displayed. They have a pair of deep eyes like those of aliens in science fiction films, composed of compound eyes made up of about 4,000 small eyes, pale purple in color, and two pairs of antennae on the head, giving a thoroughly avant-garde feel.
Among them, the largest is the giant isopod (Bathynomus giganteus A. Milne-Edwards, 1879), also known as the giant deep-sea isopod or giant isopod. The giant isopod can reach 45 cm and 1.5 kg, inhabiting the deep-sea sandy bottoms of the Pacific Ocean, Indian Ocean, and Atlantic Ocean. Its huge size makes it arguably the largest arthropod by volume in the world.
In addition, among the bycatch of bottom trawling along the coast of Taiwan, China, another kind of deep-sea sea cockroach can often be seen - the deep-sea isopod (Bathynomus doederleiniiOrtmann, 1894). This species, distributed south of Honshu, Japan, is also found in the deep-sea waters along the coast of Taiwan, China in the temperate North Pacific region, inhabiting the seafloor at depths of 150 to 600 m, with a body length of up to 15 cm, feeding on carrion in the deep-sea environment. This group of Cirolanidae animals also has seven pairs of articulated limbs, and the first pleopod is specialized into a jaw, which can send food into the jaw opening when eating. This group of scavengers in the deep-sea benthic environment can quickly find the carcasses of dead marine organisms or injured individuals that have lost the ability to move, so they were previously caught in hagfish traps or crab traps in Donggang. Usually when they encounter food, they will eat heavily, and after a full meal, they endure long periods of hunger without eating.
There are many different habitats on Earth, and various species survive in different environments in different ways of life. In the harsh intertidal environment with large day-night temperature differences and the rise and fall of tides, Ligia exotica weaves through reefs and climbs sea walls, struggling to survive amid the waves and picking up organic debris; while in the extreme environment of the cold, low-temperature deep sea, giant isopods rely on tenacious vitality and specialized physiological functions, ready at any time to feast, then entering a state of hunger after the big meal and lying in wait for the next one. The different habits of diverse species let us see more of nature's wonders and beauty.
