Marine Wonders: A Fascinating Look at 6 Unique Underwater Creatures
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Olin, North Carolina
Water covers over seventy percent of the Earth’s surface, and scientists estimate that there are between 700,000 and 1,000,000 different species living in our oceans, excluding microorganisms. Naturally, marine life has evolved to have many distinct adaptations that are not typically found in land animals, leaving us with many unique creatures, the likes of which cannot be found anywhere else but under the sea. This article will describe six of the most fascinating underwater animals.
Larvaceans
When it comes to unique sea creatures, it would be impossible to leave out larvaceans. These tunicates, a type of marine invertebrate, are known for the distinctive nets that surround their bodies, which they use to help them eat. These scavengers feed off of marine snow, a collection of organic debris made up of substances like fecal matter and decaying animal corpses.
The nets that surround larvaceans are made of a mucus composed of protein and cellulose and serve to filter food from the water, keeping particles that are too large away and letting particles that are small enough to eat through to the animal. When the net of a larvacean gathers too much large debris to be effective, the larvacean discards it and begins to make a new one, while the previous one becomes marine snow. If a larvacean is disturbed and feels threatened, it will also discard its net and begin to make a new one. Some have bioluminescent nets, and scientists suspect that they may have developed this feature as a defense mechanism, as these nets, when discarded, can create a distraction for a predator, allowing the larvacean to escape. It is estimated that a larvacean can go through up to sixteen nets in one day. However, these creatures tend to have very short lifespans, often lasting from around four to seven days.
There are three different families of larvaceans, and their nets can range from about the size of a walnut to over a meter in length, but the fragile nets of larvaceans make them difficult to collect and study, so there is much more to be learned about these unique creatures.
Siphonophores
Siphonophores are an order of marine organisms that are composed of genetically identical parts called zooids, with each considered an individual multicellular organism, but most cannot survive outside of the siphonophore colony. Zooids are specialized to perform specific functions to help the siphonophore survive, such as digestion, movement, and reproduction.
There are 175 different recognized species of siphonophores, and every species is different, but some siphonophores have reached longer lengths than whales, despite only being about as wide as a broomstick, with some scientists deeming them the longest animals on Earth.
Siphonophores can look and behave similar to jellyfish, leading many people to confuse the two animals, although they are separate animals within the same phylum, a way of classifying life. Many siphonophores are bioluminescent, attracting prey, which they then sting with their tentacles once the creature is close enough.
Many siphonophores are very fragile, breaking apart even when gently touched, which has somewhat inhibited our scientific understanding of the creatures, as they can be difficult to collect from the wild without seriously harming the organism.
Clinging Jellyfish
Clinging jellyfish are mostly known for their unusual behavior of clinging to various marine plants.
These jellyfish have, in recent years, been found in the United States, specifically New Jersey, Maine, and Massachusetts, but usually live in various parts of Asia, including Vietnam, Russia, and Japan, leaving scientists unsure of how they came to live in so many different locations.
Clinging jellyfish are very small and usually have a bell diameter of three centimeters maximum, as
well as a structure called a manubrium that appears as a brown “X” shape when viewed from above, and a minimum of sixty tentacles, each of which has sticky pads to help with clinging to plants, and nematocysts, or stinging capsules, used to attack prey.
During the night, clinging jellyfish move freely in the water, searching for food, but during the day, the jellyfish anchor to plants like seaweed and seagrass. When they feel disturbed, they will detach themselves from the plant and sting the organism that is closest to them as an act of self-defense. Clinging jellyfish live in calm, shallow, and densely vegetated areas, and are both small and primarily immobile, making them somewhat difficult to spot, leading to concern about their presence in bodies of water used by humans.
Some scientists have theorized that pollution may be causing an increase in algae, leading to an increase in algae-eating copepods, the main food source of these jellyfish, possibly explaining their sudden migration. Alternatively, the effects of overfishing may have resulted in a lack of predators for this species, allowing them to reproduce at increased rates.
Handfish
Handfish are a type of anglerfish that live exclusively in Australia, with only fourteen confirmed species, at least two of which have not been spotted in decades, leading some scientists to believe they are extinct.
Handfish live in benthic environments at the bottom of the sea, mostly located at sandy seafloors. They have a complex and poorly understood mating process, the specificity of which is believed to have contributed to the decline in population and possible extinction of multiple species. Female handfish will lay their eggs at the bases of marine plants like seagrasses and seaweeds and will stay with their eggs until they hatch.
Despite their unique mating process, what really sets handfish apart from other organisms is their anatomy. Handfish are named after their special fins, which somewhat resemble human hands, and are used to walk on the seafloor instead of swimming through the water.
Sea Robins
Sea robins have a unique appearance, behavior, and evolutionary history. Not only do they have two enlarged pectoral fins that are often said to look like wings, they have also developed six leglike appendages that they use to walk around and search for food.
These leglike fins are very sensitive, and can be used to feel the ground below them and to dig when they suspect there could be something to eat underground. The fins of sea robins are so effective at finding food due to an interesting evolutionary feature: they have papillae, organs that can experience taste. In fact, sea robins are so proficient at finding food that other organisms have been reported to follow them around, attempting to eat some of the food that they discover.
When a team of scientists was studying various species of sea robins, they made the surprising discovery that some species had no papillae on their fins at all. The species that had papillae used their fins to search for food, but the species that did not have papillae simply used their fins to walk. This fact led scientists to come to the conclusion that sea robins, or, at least, their common evolutionary ancestor, were initially unable to taste with these fins, until one species mutated to have this feature, which made it easier for them to survive and allowed them to pass it down to their offspring, leading to multiple species obtaining this feature through the process of evolution.
Another noteworthy characteristic of sea robins are the distinctive noises that they make when above water. Sea robins have specialized muscles attached to their swim bladders, organs that help underwater creatures manage buoyancy. These muscles allow sea robins to make a variety of unique sounds, including croaking, clucking, and growling, when they are removed from their underwater environment.
Snapping Shrimp
Snapping shrimp describes a wide variety of shrimp species that are known for their asymmetrical claws, many of which can create a loud snapping sound, giving them their name.
The larger of the two claws can grow to half of a shrimp's body length in some species, and the noise created by this claw can reach up to 210 decibels, which is louder than a gunshot. In fact, snapping shrimp are so loud that during World War II, American submarines were hidden in locations with snapping shrimp colonies to conceal the noise created by the submarines and equipment. Recently, scientists have discovered that the loud noise that is produced is not created by the claw itself, but from the bubble created when it is opened or closed. When a snapping shrimp opens its claw, water is able to flow inside of it, and when it is closed, the water is pushed out of the claw with so much force and speed that a small bubble is created. This bubble, which moves at around sixty miles per hour, does more than create a sound—it is so powerful and fast that small animals will die when hit with it, and larger ones will often be stunned, allowing the snapping shrimp to eat its prey without a struggle. Naturally, snapping shrimp will also create a bubble when faced with a threat, helping to deter any possible predators. Another way that snapping shrimp use these bubbles is to communicate with other snapping shrimp within a colony.
Synalpheus, one genus of snapping shrimp, are considered the only eusocial marine animals, meaning that they live in complex colonies with different roles for different members. Interestingly, some snapping shrimp are known to have mutualistic relationships with gobies. In these relationships, a snapping shrimp will allow a goby to live in its burrow, and the goby will warn the snapping shrimp about any possible predators or threats to its safety.
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