Jaekelopterus rhenaniae ("Otto Jaekel's wing from the Rhineland") is an extinct species of the Eurypterida (sea scorpions). At an estimated length of 2.5 meters (8.2 feet), it is one of the two largest arthropods ever discovered (the other is a giant millipede-like animal, Arthropleura, although which animal was larger is unclear, as well as the other eurypterid Pterygotus). It lived approximately 390 million years ago. Although called a "sea scorpion", it is speculated to have lived in fresh water rivers and lakes, and not in saltwater seas. The animal was described by Simon Braddy and Markus Poschmann of the University of Bristol in the journal Biology Letters (November 2007); they found a 46 cm chelicera (claw-like mouth part), and estimated the total size of the animal based on the proportions of this claw.
The animal's fossilized remains were discovered in the Early Devonian (Emsian) Klerf Formation Lagerstätte of Willwerath near Prüm, Germany.