Going Against the Shellshock: Horseshoe Crabs Aren't What You Think
Arachnid-like Crustaceans: Species with Spider-like Traits
Who'd've thought that the spidery-legged, armored beasts of the New Jersey shore are more closely related to arachnids like spiders and scorpions than to their fellow crustaceans? But here we are, dealing with a major shakeup in the arthropod world.
The study published in Systematic Biology in 2019 confirmed horseshoe crabs, or order Xiphosura, as arachnids. Researchers from the University of Wisconsin-Madison, Jesús Ballesteros and Prashant Sharma, analyzed the complete genomes of three horseshoe crab species and more than 50 different arthropod species to arrive at this conclusion. Regardless of the analysis method, the horseshoe crab always fell under the arachnid branch of the family tree.
In an official statement, Ballesteros mentioned, "Our findings indicate that horseshoe crabs are part of the arachnid radiation, not just a group closely related but independent of arachnids. This is a significant shift in our understanding of arthropod evolution."
Horseshoe Crabs: Arachnids in Disguise
Horseshoe crabs, with a body divided into three main parts — the cephalothorax, abdomen, and telson — are chelicerates, a subgroup of arthropods. They lack mandibles, relying on their chelicerae, which act as fangs or pincers. This structure, along with the shared absence of mandibles, makes them more akin to arachnids.
Generally, crustaceans—the aquatic cousins of horseshoe crabs—sport mandibles and various appendages depending on the species. However, the idea that horseshoe crabs and crustaceans belong to the same family has been a long-held misconception, as their genome is more similar to arachnids. The discovery has massive implications for the evolution of arachnids, necessitating a revision of all previous hypotheses on the evolution of arthropods.
What's Next for Arthropod Research?
With horseshoe crabs solidified as arachnids, scientists must dig deeper into the shared evolutionary history of these creatures. The study marks a significant milestone in understanding arthropod diversity and the complexity of their genetic relationships. So, don't be surprised if the next time you spot those familiar-looking horseshoe crabs on the shore, you see them with new eyes.
Horseshoe crabs, previously thought to be closely related to crustaceans due to their physical resemblance, have been reclassified as arachnids, following a groundbreaking study in science, particularly in the field of biology, which was published in Systematic Biology in 2019. This reclassification could lead to further exploration of medical-conditions related to arachnids and the role of technology in unraveling complex genetic relationships among different species of arthropods.
