Arthropleura is a 6–10 feet long about 20 feet long in the series relative of centipedes and millipedes native to the Upper Carboniferous of Britain and the United States. It's the largest known land invertebrate of all time and grew so large because of the high percentage of oxygen in the Earth's atmosphere at that time. They have poor eye sight but have an excellent sense of smell and touch.
One came through an anomaly and killed a cleaner and poisoned Stephen, who fortunately survived. The Arthropleura later burrowed through the wall into an electrical room. Cutter harvested venom from its bite in order to create an anti-venom to heal Stephen. While struggling to get a wire off of its head that Conner got on it, the Arthropleura slams the wire into an electric circuit box, electrocuting it. It them plummets off the balcony and dies.
An Arthropleura is captured for use in Leek's creature army, but how it survived without the Carboniferous atmosphere it needed to live is unknown. When the security system holding it failed, it ran amok. It was presumably killed when the creatures were lured into a locked room where they all killed each other.
The body of the Arthopleura is composed of 30 plates, with each having a pair of legs under them. The Arthopleura could be 10 feet long, and is the largest arthropod discounting the Silurian Scorpion. It is very fast and easily manouvered through trees and logs. There are 2 types of Arthopleura and about 300 million years ago they went extinct.
The Arthropleura in Primeval are herbivorous and don't eat their human victims once they have poisoned them. They are related to both the herbivorous millipedes and the carnivorous centipedes, so its diet has been a debate among scientists, and because of its powerful pincers, it used to be thought that Arthropleura was primarily a carnivore. Though new discoveries show that it was a herbivore in real life, and maybe the Arthropleura in Primeval only used its venom for defense. In Primeval, when researching the creature, Connor Temple says that "the creature would eat dead organisms, water and leaves".
―The team are surprised to learn the creature is venomous
They have powerful pincers and a venomous bite and can easily be provoked into attacking. 
Symptoms of Arthropleura poisoning include:
Uncontrolled shaking
Anaphylaxis
Short term memory loss in recovered patients
Once bitten the venom then begins to slowly attack the central nervous system, not so far removed from modern biochemistry as to be totally ineffective and any enzyme inhibitor would be detrimental to an extent. But being detritus eaters, they make no attempt to eat their victims.
Eoarthropleura the Silurian ancestor of the Arthropleura appears in 2.5.
Arthropleura is often confused with a creature resembling a Giant Millipede that appeared in a Promotional Poster in which Nick and Abby are surrounded by the Giant Arthropod. The markings on the cuticle and its large size show its not the Arthropleura the creature appears to be trying to constrict them like an Anaconda. The creature is referred to as Millipede.
Arthropleura is the 1st venomous creature in Primeval
Arthropleura is the 1st dangerous herbivorous creature in Primeval
The Arthropleura is different from the creatures seen in the fossil record in addition to the Arthropleura in Walking with Monsters and Prehistoric Park. For dramatic effect, the Arthropleura is heavily re-imagined by the producers as it was venomous, larger than the real animal, and highly aggressive. Its unusually aggressive attitude is explained by Connor and Claudia as they theorize this one in particular suffers from a personality disorder when Connor says it's timid.
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Added by MrThermomanPreacher
