What is the largest arachnid that has ever lived? -

The term “arachnids” probably conjures up visions of spiders: from creepy, creepy things spinning silently from webs in the corner of the room to large, hairy creatures with fangs – like the mythical Shelob or Aragog – stalking you in the dark. . But just how big (and fierce) can these arachnids get? Better yet, who was the greatest to have ever lived?

Answering this question is deceptively simple. Arachnids are eight-legged arthropods, which means that this group contains not only spiders but also scorpions and ticks among others, much smaller and rarer groups. Of these, spiders are the most diverse group of arachnids (the 50,000th species was recently discovered, and this number should increase). The problem is that exactly what counts as an arachnid is a bit of an open question.

Arachnids are part of a larger group of arthropods called chelicerae. The chelicerae are subdivided into smaller groups, with the arachnids being one group and the horseshoe crabs (in the order Xiphosura) and sea scorpions (Eurypterida) being separate but related to the arachnids.

According to Russell Bicknell, a paleontologist at the University of New England in Australia, this is the traditionally accepted phylogeny. But one paper came out recently that suggested that was wrong, and suggested that horseshoe crabs and sea scorpions actually nest in arachnids.”

Related: Why do Cambrian creatures look so weird? The Eurypterids, shown here in this illustration, were the largest species of arachnid to ever live, rivaling humans in size.

The Eurypterids, shown here in this illustration, were the largest species of arachnid to ever live, rivaling humans in size. (Image credit: estt/Getty Images)

Thomas Hegna, assistant professor of paleontology at the State University of New York (SUNY) in Fredonia, who was not involved in the new study, told Live Science in an email that the new phylogeny, based on molecular analysis, implies some terrestrial chelicerae groups (spiders and scorpions) predated marine groups (horseshoe crabs and sea scorpions). However, despite the fact that this claim is well supported by genetic evidence, it is inconsistent with the fossil record.

This may sound like paleontological pedantry, but it actually makes a huge difference when it comes to determining the largest arachnid of all time.

According to the traditional view of the arachnid family tree (ignoring horseshoe crabs and sea scorpions), the largest living arachnid is probably a spider.

There are two spiders that make great contenders for the title of “World’s Largest Spider”. The largest known spider by mass is the Goliath Bird Eater (Theraphosa blondi)a 6-ounce (170-gram) spider whose body can reach up to 5 inches (12 centimeters) in length, a number that reaches 11 inches (28 cm) when its legs are included, according to the American Association for the Advancement of science (AAAS).

If one is to judge the size of a spider instead by the diameter of its leg span, then the largest spider could very well be the giant hunter spider (Maxima heteropodslisten)), which has a leg span of about 1 foot (30 cm) in diameter, making it about the size of a dinner plate. Despite its size, this spider was only discovered in 2001.

When we delve into the fossil record, we find that the largest arachnid of all time was probably not a spider, but a scorpion. Brontoscorpion anglicus was a scorpion that lived during the Silurian-Devonian era (between 350 million and 450 million years ago) and reached lengths of almost 3 feet (1 m) long – five times longer than the longest living scorpion today. However, the caveat here is that the only example of this species was described from a single fossilized finger, so the true size of the animal is an educated guess.

Related: Is each spider web unique?

These animals are the largest known arachnids, both living and extinct, as arachnids are traditionally defined. But if sea scorpions and the horseshoe crab are indeed considered arachnids, as new research might suggest, then the largest living arachnid is no longer a spider, but rather a horseshoe crab.

The largest living species of horseshoe crab, Tachypleus tridentatus, could reach 31 inches (79.5 cm) in diameter.

The largest living species of horseshoe crab, Tachypleus tridentatus, could reach 31 inches (79.5 cm) in diameter. (Image credit: Jaap Bleijenberg / Alamy)

The largest living species of horseshoe crab surpasses the largest living spiders. Tachypleus tridentatus, the largest of this group, can reach heights of 31 inches (79.5 cm) and weigh up to 9 pounds (4 kilograms), according to a 2017 study published in the Asia-Pacific Biodiversity Journal.

As for the largest species of all time, the title would likely go to a member of the now-extinct sea scorpions, a group scientifically known as the eurypterids. Fossils suggest that many of these ancient marine predators even rival humans in size.

The largest species in this group was Jaekelopterus rhenaniae, a species discovered in 2007 that had claws up to 18 inches (46 cm) long. From the claws, researchers estimated that its body was about 8 feet (2.5 m) long, making it not only the largest potential arachnid, but the largest member of the entire group that contains spiders. arachnids, chelicerae.

Originally posted on Live Science.

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