Megarachne.
Megarachne was a predatory freshwater arthropod of the order of eurypterids, often called sea scorpions. Two fossil specimens of the genus have been discovered, in San Luis, Argentina, in deposits of Late Carboniferous age from the Gzhelian stage. Megarachne ("great spider") was initially misidentified as a spider. With a body length of 54 cm (1.77 ft), it was a medium-sized eurypterid, similar to others within the Mycteropoidea, a rare group known primarily from South Africa and Scotland. The mycteropoids evolved a specialized method of feeding referred to as sweep-feeding, raking through the substrate of riverbeds to capture and eat smaller invertebrates. Due to their fragmentary fossil record and similarities between the genera, Megarachne and two other members of its family, Mycterops and Woodwardopterus, have been hypothesized to represent different developmental stages of a single genus.
