Two Eurypterids prowling the waters of Acheron.

Eurypterids are a group of aquatic arthropods closely related to scorpions. They inhabit seas all around the Prime Material Plane, although their only detected habitat in known space is in Acheron. Eurypterids are usually either very small, or medium sized.

The largest Eurypterid Jaekelopterus, reached 2.5 meters (8.2 ft) in length. Eurypterids were not uniformly large and most species were less than 20 centimeters (8 in) long; the smallest eurypterid, Alkenopterus, was only 2.03 centimeters (0.80 in) long.

Eurypterids are either mesopredators or apex predators depending on their size, although even Eurypterids considered apex predators are still hunted by larger creatures. The Empire’s national animal is a Eurypterid, specifically the Jaekelopterus.


Eurypterids, in a similar manner to cimexians and other arthropods, possess segmented bodies and jointed appendages. These are covered in a cuticle composed of proteins and chitin. As in other chelicerates, the body is divided into twin tagmata; being the frontal prosoma and the hind opisthosoma. The frontal prosma was covered by a carapace shield, which the compound eyes and ocelli are situated.


Depending on size, Eurypterids can be either higher ranking mesopredators or powerful apex predators. In the case of smaller Eurypterids, they can be considered prey to almost any relatively large aquatic organism. Eurypterids are mostly ambush predators, although some are highly aggressive and will chase down prey.

In some scenarios, certain Eurypterids are capable of limited terrestrial locomotion.

While the killing of Jaekelopterus is forbidden via religious law, other Eurypterid species are hunted and considered a delicacy. They are sometimes placed in tanks and considered exotic pets, and in one case a Cimexian unleashed a swarm of them into a kindergarten.