Megarachne

Megarachne is a genus of eurypterid, an extinct group of aquatic arthropods. Fossils of Megarachne have been discovered in deposits of Late Carboniferous age, from the Gzhelian stage, in the Bajo de Véliz Formation of San Luis, Argentina. The fossils of the single and type species M. servinei have been recovered from deposits that had once been a freshwater environment. The genus name comes from Ancient Greek μέγας (mégas), meaning "great", and ἀράχνη (aráchnē), meaning "spider", and thus, "great spider"; because the fossil was misidentified as a large, prehistoric spider. With a body length of 54 cm (21 in), Megarachne was a medium-sized eurypterid. If the original identification as a spider had been correct, Megarachne would have been the largest known spider to have ever lived. Eurypterids such as Megarachne are often called "sea scorpions", but the strata in which Megarachne has been found indicates that it dwelled in freshwater and not in marine environments. Megarachne was similar to other eurypterids within the Mycteropoidea, a rare group known primarily from South Africa and Scotland. The mycteropoids had evolved a specialized method of feeding referred to as sweep-feeding. This involved raking through the substrate of riverbeds in order to capture and eat smaller invertebrates. Despite only two specimens having been recovered, Megarachne represents the most complete eurypterid discovered in Carboniferous deposits in South America so far. Due to their fragmentary fossil record and similarities between the genera, some researchers have hypothesized that Megarachne and two other members of its family, Mycterops and Woodwardopterus, represent different developmental stages of a single genus.