What is "pentecopterus"

Pentecopterus is an extinct genus of sea scorpion that lived during the Ordovician period, as early as 467.3 million years ago. One species is P. decorahensis. It is the oldest described eurypterid, and, at an estimated length of up to , one of the largest known arthropods ever discovered, similar in size to the famous millipede-like Arthropleura. Other notable sea scorpions include the more recent Silurian-aged Acutiramus, and Devonian Jaekelopterus, the only arthropod currently known to surpass P. decorahensis in size. According to researcher James Lamsdell of Yale University, P. decorahensis "is the first real big predator".