Description

Megarachne is a genus of eurypterid, an extinct class of aquatic arthropods. Fossils belonging to Megarachne have been unearthed from Late Carboniferous deposits, specifically from the Gzhelian stage, located within the Bajo de Véliz Formation in San Luis, Argentina. The single and type species, M. servinei, is represented by fossils found in environments that once comprised freshwater habitats. The genus name is a composite of two Ancient Greek terms, "megas" meaning "great" and "arachne" meaning "spider," thus translating to "great spider." This nomenclature originated from the erroneous initial classification of the fossil as a large prehistoric spider.

Measuring at 54 cm (21 in) in body length, Megarachne stood as a moderately-sized eurypterid. If the initial identification as a spider had been accurate, Megarachne would have held the distinction of being the largest documented spider in existence. Despite the frequent designation of eurypterids like Megarachne as "sea scorpions," the geological strata housing Megarachne's remains suggest that its habitat was freshwater rather than marine.

Feeding habits

Megarachne had blade-like formations on its limbs that enabled it to employ a feeding strategy called sweep-feeding. This involved using its front appendage blades to comb through the pliable sediment of watery habitats like swamps and rivers. By doing so, it could apprehend and consume small invertebrates.

Misconceptions

Initially, when the specimen was unearthed, it was believed to belong to a spider. However, in 2005, Paul Seldon, José Corronca, and Mario Hünicken re-evaluated the specimen, along with another one, and concluded that it was, in fact, an eurypterid. Eurypterids, often called sea scorpions, share kinship with arachnids and boast four pairs of legs, which can make their fossilized remains resemble spiders. While not a colossal spider, Megarachne has proven to be a remarkable find. As an eurypterid, it exhibits distinctive morphological characteristics that set it apart from its counterparts within the same family.