… an extinct genus of sea scorpions. They existed during the Silurian Period, from around 432 to 418 million years ago. There are fifteen species belonging to the genus Eurypterus, the most common of which is Eurypterus remipes, the first eurypterid fossil discovered.
Until recently, eurypterids were thought to belong to the class Merostomata along with order Xiphosura. It is now believed that eurypterids are a sister group to Arachnida, closer to scorpions and spiders than to horseshoe crabs.
Members of Eurypterus averaged at about 5 to 9 in (13 to 23 cm) in length, but the largest individual discovered was 1.3 m (4.3 ft) long. They all possessed spine-bearing appendages and a large paddle they used for swimming. They were generalist species, equally likely to engage in predation or scavenging.
(read more: Wikipedia) (image: Dimitris Siskopoulos)