Megalograptidae are a family of eurypterids, an extinct group of chelicerate arthropods commonly known as "sea scorpions".

The megalograptids were likely the first major successful group of eurypterids, evidenced by a Late Ordovician radiation.

The first and third pairs of walking legs are short, with diverging or closely spaced spines.

[2] The Megalograptidae are thought to be relatively primitive (between the genus Onychopterella and the Eurypteroidea) because they lack the synapomorphy of all more derived swimming eurypterines; namely, the modified distal margin of the sixth podomere of the swimming leg.

Though such a position has never been recovered in phylogenetic analyses and is primarily based on this missing characteristic (along with other primitive characters), the clade might instead be placed between the Eurypteroidea and the Mixopteroidea.