How Are Lobsters And Scorpions Related?

To determine whether lobsters and scorpions are related, you have to go way back in the fossil record. Humans weren’t even around when the first scorpions and lobsters existed some five hundred million years ago. There are suggestions in the fossil record that they had some common ancestors in the distant past.

Lobsters and scorpions are only distantly related to each other. They both belong to the phylum Arthropoda, that emerged in the Cambrian explosion some 541 million years ago. They diverged as they evolved into different sub-phyla, the Crustaceans, and the Chelicerata, respectively.

Arthropoda is the biggest phylum in the animal world and includes insects, millipedes and centipedes, arachnids such as scorpions and spiders, and crustaceans such as crabs and lobsters. The horseshoe crab has recently been recognized as being an arachnid, and so it is more closely related to scorpions than lobsters are.

The Similarities and Differences Between Lobsters and Scorpions

Lobsters and scorpions have some obvious similarities even to the untrained eye. They both have a large pair of front pincers called chelae used for grasping and catching prey; they both have segmented bodies and segmented legs that grow in pairs, and they both molt as they grow. 

Lobsters and scorpions have eight legs for walking in addition to their specialized pair of legs ending in claws. Technically they have ten legs as scientists count their front appendages as legs too. For this reason, lobsters are called decapod (ten-legged) crustaceans, along with crayfish and crabs.

Lobsters live in aquatic, marine environments, while scorpions are primarily terrestrial. Millions of years ago, this wasn’t always the case. Giant prehistoric scorpions lived in the sea in ages past. Lobsters, unlike scorpions, do not possess venom, and their tails don’t end in a stinger poised to administer it. 

Although they are both members of the Arthropoda phylum, lobsters belong to the sub-phylum Crustacea while scorpions belong to the sub-phylum Chelicerata, which consists of arachnids. Insects also belong to the phylum Arthropoda. All arthropods, including lobsters and scorpions, produce eggs, but scorpions don’t lay their eggs. The mother keeps them inside her body until the scorplings hatch and emerge onto her back.

Lobsters are crustaceans, along with crabs, crayfish, krill, shrimp, and barnacles. Most crustaceans are aquatic, but a few, like woodlice, are terrestrial. Spiders, ticks, mites, and scorpions belong to the Chelicerata group and are all classified as arachnids. They live primarily on land.

Scientists have recently confirmed that horseshoe crabs are arachnids and belong with spiders, scorpions, and ticks rather than with the crustaceans. Studies of the horseshoe crab’s genome have repeatedly shown that they are related to arachnids and breathe with book gills that resemble the book lungs of scorpions and spiders. 

Lobsters and crabs have brains similar to insects and, like them, have a mushroom-shaped structure. A study in 2020, led by a scientist at the University of Arizona, reports that the neuroanatomical features of the mushroom body brain structure, which was thought to be restricted to insects, are also present in crustaceans. 

The study showed that while the mushroom bodies in crustacean brains seem more diverse than those of insects, they contain the same neuro-anatomical elements. Insects are in a different sub-phylum to scorpions and lobsters called Hexapoda because they have six legs. Mushroom bodies are also found in scorpion and spiders’ brains, which suggests that they all had some ancestors in common millions of years ago.

What Is An Arthropod?

The word “Arthropod” means “jointed feet” because arthropods’ body segments bear jointed appendages such as legs, feelers, and arms with pincers.

An arthropod is an animal that doesn’t have an internal bony skeleton like humans and other mammals. It is an invertebrate which means it lacks a backbone. An arthropod’s soft inner body is held together by an exoskeleton made of a rigid external material called chitin. The animal’s body grows inside its chitinous exoskeleton until it no longer fits. Then it molts and emerges with a new exoskeleton that usually takes a few hours to harden. 

Some exoskeletons are reinforced with calcium carbonate that makes them even stronger and harder. People usually refer to these as shells. Lobsters and crabs molt throughout their lives, but other arthropods only molt until they reach adulthood or sexual maturity.

Many land and sea animals are arthropods. They have a segmented body and paired, jointed appendages. Arthropoda is an enormous phylum and makes up eighty-four percent of all known species. 

Arthropoda is divided into the subphyla Crustacea, Chelicerata, Hexapoda, and Myriapoda, which contain crustaceans, arachnids, insects, and millipedes and centipedes, respectively. Lobsters are crustaceans, while scorpions are arachnids (Chelicerata). The vast majority of crustaceans are marine dwelling animals, while arachnids are mainly terrestrial, i.e., land-dwelling. Horseshoe crabs and sea spiders are marine chelicerates.

The earliest known fossil scorpions were aquatic animals. In a 2015 article published in the scientific journal Nature, the authors described an extinct giant sea creature that existed around four hundred and eighty million years ago. It had modified legs, a filter system for feeding, and gills on its back, and they called it Aegirocassis benmoulae. It reached at least seven feet in length and was one of the biggest arthropods that ever lived. 

It belongs to the anomalocaridid family, most of which had a pair of grasping appendages at the front used to catch prey. They are distant ancestors of scorpions and lobsters. Anomalocaridids are all now extinct. The Aegirocassis fossil was found in Morocco, and its head appendages were modified into a filter-feeding apparatus which meant that it could live on plankton.

In 2015, another scientific article described a giant sea scorpion named Pentecopterus decorahensis after a warship used in ancient Greece. According to the Yale University research team, it could grow to almost six feet and had giant pincer-like limbs for grasping its prey. It dates back to four hundred and sixty-seven million years ago and is the oldest eurypterid ever described. 

Eurypterids (Eurypterida) were a group of aquatic arthropods that are ancestors of arachnids, i.e., spiders, scorpions, and ticks. They are usually referred to as sea scorpions, but only the earliest ones lived in the sea. Others that occur later in the fossil record lived in brackish or even fresh water and were not true scorpions. 

However, they all possessed jointed appendages and segmented bodies covered with a cuticle made of chitin and protein, just like other arthropods. They had a skinny tail that looks like the makings of a stinger but without the curve. They varied in size from a couple of centimeters to around two and a half meters in length and were chelicerates, like modern scorpions and spiders.

Scientists have said that the discovery of Pentecopterus showed that eurypterids evolved ten million years earlier than was previously thought. It was a sizeable predatory arthropod with a large head shield and narrow body. The fossil was found in a fossil-rich meteorite crater in Iowa by geologists from the University of Iowa, which contained both juvenile and adult specimens.

Pentecopterus lived in shallow marine waters. Another genus of eurypterids called Jaekelopterus is the largest known arthropod to have ever existed and had claws that were almost half a meter long. Scientists believe that it lived in fresh water and reached a size of just over two and a half meters. 

The Evolution Of Scorpions

Researchers who have mapped the genomes of spiders and scorpions say that they evolved from a common ancestor over four hundred million years ago. The oldest scorpion species known to science is from fossils dating back four hundred and thirty-seven million years and is called Parioscorpio venator. It was an arachnid, and its species name, Venator, means “hunter”. The fossils were discovered in 1985 near Waukesha in Wisconsin.

This scorpion was small, only around two and a half centimeters long. It shows an evolutionary link between the way scorpions breathed underwater, before they evolved as land-dwellers, and how modern scorpions breathe. It lived in the Paleozoic era. When it was examined under a microscope, scientists found they could identify a circulatory and respiratory system the same as the one in modern scorpions, as well as a chamber where its venom was stored.

Its circulatory-respiratory system is identical to that of air-breathing arachnids but is also very similar to that of marine-dwelling horseshoe crabs. It shows that while ancient scorpions initially lived underwater, they had already developed the biological structures necessary to live on land and could easily make the transition. The Waukesha region was once a shallow, warm ocean four hundred and fifty million years ago. 

Scientists are uncertain whether Parioscorpio lived on land or in water but argued that given that its internal anatomy resembles that of today’s scorpions, it could have lived on land, at least for the time it took to mate and spawn. This is what horseshoe crabs do today. However, the fact that the fossils were found with other marine specimens suggests that it could have been aquatic.

There is a rich scorpion fossil record, and scorpions are the oldest arachnids ever found. Scientists believe that Chelicerata evolved from marine organisms around four hundred and forty-five million years ago. They are related to the eurypterids of which more than two hundred and forty species have been identified. Although they are now extinct, there is some evidence that a few eurypterids may have adapted to living on land. 

Some scientists don’t believe that they are related to modern scorpions. Other scientists say that given what they know about the fossil record, scorpions almost certainly evolved from the Eurypterida, or water scorpions since they share common morphological characteristics. The fossil record is fragmented, and it’s possible that many more types of scorpions existed that scientists don’t know about.

Scorpions are sometimes described incorrectly as living fossils because they are still similar in many ways to the fossils of their ancestors that go back millions of years. However, scorpions have undergone many significant physiological, behavioral, biochemical, and ecological changes that ensured their survival to the present day. There are still many gaps in the understanding of scorpion evolution. 

All scorpions living today have venom glands. The telson in a scorpion is the end part of the tail where the stinger (aculeus) is located, and it is evident in scorpion fossils from the Palaeozoic, Mesozoic, and Cenozoic eras. Eurypterids also had telsons, but they were thought to use the serrated spiny tips to slash and pierce their prey rather than sting it. A fossilized eurypterid called Slimonia acuminata with a spiny tail curved to one side is believed by scientists to attack and kill its prey with sidelong strikes.

Lobsters use their tails as paddles to help them swim by flipping them up and down vertically, but eurypterid’s tails could only move horizontally. Sea scorpions could slash their tails from side to side while holding their prey with their sharp front claws. Sea scorpions are not believed to have had venom glands and killed their prey with biomechanical rather than biochemical means.

The Evolution of Lobsters

Half a billion years ago, an event called the Cambrian explosion gave rise to the Arthropoda genus. Within that genus is the sub-category Crustacea which includes lobsters. The Cambrian explosion refers to an era when all major animal phyla started to appear in the fossil record. It produced arthropods with compound eyes and segmented legs. Scientists still argue about what sparked this explosion of life. 

The ancestors of lobsters existed before dinosaurs roamed the Earth, and one of the oldest known is an animal called Yawunik kootenayi. It could whip its front claws around and fan them out for an attack but retracted them under its body when swimming and was only a few inches long. It is an early arthropod from the Cambrian period with four eyes and is thought to have lived five hundred and eight million years ago before the first fish existed.

The oldest lobster fossil found to date was discovered in Mexico and is around one hundred and twenty million years old. It belongs to the same genus that still occurs in Africa to this day. This is because Africa and South America were once joined and split apart at around this time.

Lobsters vary widely in their morphology, even though their body structure looks similar. There are clawless and clawed lobsters, blind and sighted lobsters, freshwater and sea lobsters who live at various depths from shallow water to the deep ocean. Lobsters, unlike scorpions, never stop growing throughout their long lives. Scientists don’t know just how large they can get because they don’t show any signs of aging. 

Ever wondered if lobsters can survive on land? Or why they scream as they boil in a pot? Here’s an article I wrote answering that question and other facts about lobsters as well!

The Pleocyemata group of crustaceans, including lobsters, crayfish, polychelidan lobsters, crabs, and caridean shrimp, has an unusual reproductive strategy. The females keep their fertilized eggs on their abdominal appendages and don’t just release them into the sea. Polychelidan lobsters were long thought to be extinct since they only appeared in the fossil record, but they have since been found living in the deep sea.

Scientists in 2020 reported the discovery of a polychelidan lobster fossil with hundreds of eggs still attached to the underside of her abdomen. It is a new species of lobster, palaeopolycheles nantosueltae, and shows that the brood size of polychelidan lobsters has remained unchanged since the Jurassic era. The similarity between a mother scorpion carrying her young on her back and a mother lobster holding her eggs under her abdomen is reminiscent of their distant relationship.

Common Ancestors Of Lobsters And Scorpions

In 2013, scientists traced a common ancestor of lobsters and scorpions with large front pincers that goes back five hundred and five million years in the fossil record. They named it Kootenichela deppi after Johnny Depp, the actor who played the lead role in the film Edward Scissorhands. It belongs to a group of arthropods called the megacheirans, which means “great appendage”. 

Kootenichela deppi was a sea creature that lived in shallow water off the coast of British Colombia, Canada. Five hundred million years ago, it was situated closer to the equator than it is now, so the sea temperature was a lot warmer. 

Kootenichela was only around 4 cm long and had many legs like a millipede that carried it across the seafloor. Its compound, fly-like eyes were on top of mobile stalks called peduncles so that it could look this way and that for food and predators. Scientists believe its elongated claws were used to capture prey or help it probe the sandy seafloor for food. 

Aegirocassis benmoulae is thought to be a common ancestor of lobsters and scorpions and lived four-hundred and eighty million years ago. Another fossilized creature, a megacheiran called Leancholia illecebrosa, dates from five hundred and twenty million years ago and is thought to be a distant relative of scorpions and spiders. It had front appendages like forceps but was shaped a bit like a spider, and its nervous system was very different from that of crustaceans. 

Conclusions

Lobsters and scorpions are related by the fact that they are both arthropods. Still, their families diverged millions of years ago, and they have evolved into two very distinct kinds of animals. Scorpions aren’t any more closely related to lobsters than insects or millipedes, which are also arthropods. Lobsters and scorpions have several features in common, but they also have marked differences that set them apart. 

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