The largest eurypterid, and the largest known arthropod ever to have lived, is "Jaekelopterus rhenaniae". A chelicera from the Emsian Klerf Formation of Willwerath, Germany measured in length, but is missing a quarter of its length, suggesting that the full chelicera would have been long. If the proportions between body length and chelicerae match those of its closest relatives, where the ratio between claw size and body length is relatively consistent, the specimen of "Jaekelopterus" that possessed the chelicera in question would have measured between , an average , in length. With the chelicerae extended, another meter (3.28 ft) would be added to this length. This estimate exceeds the maximum body size of all other known giant arthropods by almost half a meter (1.64 ft) even if the extended chelicerae are not included. Two other eurypterids have also been estimated to have reached lengths of 2.5 metres; "Erettopterus grandis" (closely related to "Jaekelopterus") and "Hibbertopterus wittebergensis", but "E. grandis" is very fragmentary and the "H. wittenbergensis" size estimate is based on trackway evidence, not fossil remains.