Invertebrates lack backbones. They are incredibly diverse, thriving in nearly every ecosystem on Earth. However, while we are familiar with common invertebrates like mollusks, spiders, and insects, some defy expectations. There are unusual invertebrates whose behavior, appearances, and adaptations are outright bizarre. From the vibrant, leaf-like sea slugs to alien-like deep sea creatures, the list of unusual invertebrates is endless. We explore some of the popular ones below:
1. Peacock Mantis Shrimp
Scientifically called Odontodactylus scyllarus, the peacock mantis shrimp has many other names, depending on location and culture. It is commonly referred to as clown mantis shrimp, rainbow mantis shrimp, painted mantis shrimp, harlequin mantis shrimp, or simply mantis shrimp.
However, the creature’s many names isn’t the only intriguing thing about it; its appearance is, too. Peacock mantis shrimps are primarily green with orange legs, not to mention their leopard-like spots. While some consider the mantis shrimp a dangerous pest, others prize it, especially in the marine aquarium trade.
Fun fact: Peacock mantis shrimps can see polarized light and have 16 types of color receptors (humans have 3). Also, they have a mighty and fast “punch.” Researchers say mantis shrimps can break aquarium glass, with the “punch” accelerating faster than a bullet.
2. Leaf Sheep
Leaf sheep are some of the most unusual invertebrates. Besides their leaf-like appearance, the sea creatures can perform photosynthesis through kleptoplasty. As for their looks, leaf sheep have two dark eyes and two rhinophores emerging from the top of their heads. This makes them resemble a cartoon sheep covered in leaves.
3. Velvet Worm
Velvet worms look like a combination of worms and caterpillars. They are elongated with soft bodies and many legs. Apart from their distinct physical appearance, velvet worms have a unique hunting style. They spray their prey with a sticky, glue-like substance, making them immobile.
4. Horseshoe Crab
Interestingly, even with their appearance, horseshoe crabs aren’t crabs or even crustaceans, for that matter. Instead, they are chelicerates, closely related to ticks and spiders, among other arachnids.
The horseshoe crab’s unique appearance makes it an unusual invertebrate. Its body is divided into the cephalothorax (the biggest), telson, and abdomen. The creature’s internal organs, limbs, and eyes are at the cephalothorax. Because of their unique physique, horseshoe crabs are sometimes called “living fossils.”
5. Tardigrades
Tardigrades are sometimes colloquially referred to as moss piglets or water bears. They are microscopic invertebrates with pudgy, segmented bodies and clawed legs. Tardigrades can enter cryptobiosis, where they “shut down” and return when conditions improve.
While their physical appearance is strikingly odd, their resilience makes tardigrades unusual invertebrates. They can survive extreme conditions, including excess pressure, sweltering heat, and air deprivation. Researchers say that the creatures can even survive outer space.
6. Sea Pig
Sea pigs (Scotoplanes) are sea cucumbers that resemble sea pigs. They have soft, bloated bodies and tubular feet. To defend themselves, sea pigs have a toxic chemical called holothurin on their skin, which can poison other creatures.
Fun fact: Sea pigs breathe through their anus because they have poorly developed respiratory systems.
7. Giant Isopod
Prevalent in the cold, deep waters of the Indian, Pacific, and Atlantic oceans, giant isopods are unusual invertebrates because of their appearance. Although they are of little interest to most commercial fisheries, giant isopods are known to attack and destroy fish caught in trawls.
Another aspect that makes giant isopods unusual invertebrates is that they rely on scavenging dead bodies that sink to the ocean floor. Since this doesn’t happen often, giant isopods can go for years without eating.
8. Christmas Tree Worm
True to their name, Spirobranchus giganteus are commonly known as Christmas tree worms because they hugely resemble the plants. They have tubular, segmented bodies covered with chaetae. The creatures use the spiral-shaped appendages to breathe and catch food particles in water. Most Christmas tree worms live in coral reefs. They retract into their burrows for protection when threatened.
The Key Takeaway
With the majority of our planet still unexplored, especially when it comes to living organisms, it’s not surprising that new, unusual invertebrates continue to be discovered. Most of the spineless creatures inhabit the oceans and are characterized by alien-like physical features. They also have interesting hunting habits and internal organs. Giant isopods, Christmas tree worms, and velvet worms are perfect examples of unusual invertebrates.
