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

According to a 2024 paper, this family may be paraphyletic, containing modern scorpions.

[1] However, the vast majority of phylogenetic analyses classify scorpions as arachnids, not eurypterids, making this claim unlikely.

[2] Mixopterids were characterized by large exoskeletons with scattered tubercles or semicircular scales.

The third and fourth walking legs were moderately sized, with short spines.