Though originally described as a giant spider, a multitude of features support the classification of Megarachne as a eurypterid. Among them, the raised lunules (the vaguely moon-shaped ornamentation, similar to scales) and the cuticular sculpture of the mucrones (a dividing ridge continuing uninterrupted throughout the carapace, the part of the exoskeleton which covers the head) are especially important since these features are characteristic of eurypterids.Megarachne possessed blade-like structures on its appendages (limbs) which would have allowed it to engage in a feeding method known as sweep-feeding, raking through the soft sediment of aquatic environments in swamps and rivers with its frontal appendage blades to capture and feed on small invertebrates.
Although initially portrayed as a massive spider, numerous characteristics confirm that Megarachne is actually an eurypterid. Key features include the elevated lunules (moon-like protrusions resembling scales) and the cuticular texture of the mucrones (a continuous ridge along the carapace), which are distinctive to eurypterids. Additionally, Megarachne had blade-like appendages on its limbs, enabling it to employ sweep-feeding, using its frontal blades to scour through soft sediment in aquatic environments.