Eurypteridi

Eurypteridi, commonly called sea scorpions, are an extinct order of aquatic chelicerate arthropods that lived from the Ordovician to the Permian (roughly 470–250 million years ago). Fossils have been found worldwide, with rich discoveries in Silurian deposits of Gotland and North America. Eurypterids ranged from small, shrimp-like forms to giant predators, with Jaekelopterus rhenaniae among the largest arthropods known, possibly exceeding 2 meters in length.

Morphology: Eurypterids possessed a dorsoventrally flattened body consisting of a broad prosoma (head and thorax) and an articulated opisthosoma (abdomen). The head bore pair of chelicerae used for seizing prey, followed by pedipalps and four to six pairs of walking appendages. In many groups, the abdomen ended in a long, sometimes spiny telson. Some lineages developed large, spined chelicerae and broad swimming limbs for propulsion, suggesting a variety of aquatic lifestyles from swimmers to ambush predators.

Ecology: They inhabited shallow seas, estuaries, and freshwater environments. They were active predators, feeding on smaller arthropods and fish-like organisms, aided by their grasping appendages and, in some taxa, powerful chelicerae.

Taxonomy and legacy: Eurypterida is an extinct order within Chelicerata, related to arachnids such as spiders and scorpions. They declined through the Late Paleozoic and disappeared by the end of the Permian mass extinction. Their fossil record sheds light on Paleozoic marine ecosystems and the evolution of chelicerates.