Adelophthalmidae

Adelophthalmoidea (the name deriving from the type genus Adelophthalmus, meaning "no obvious eyes") is a superfamily of eurypterids, an extinct group of aquatic arthropods. Adelophthalmoidea is classified within the infraorder Diploperculata, in the suborder Eurypterina. The superfamily contains four families: Adelophthalmidae, Nanahughmilleriidae, Parahughmilleriidae, and Pittsfordipteridae.''''

Adelophthalmoid eurypterids were small and swimming eurypterids that appeared in the Silurian period. With the earliest known members of the group, Nanahughmilleria prominens and Parahughmilleria maria, being known from deposits of Early Silurian (possibly the Llandovery epoch) age and the last members, belonging to the long-lasting and widespread genus Adelophthalmus, going extinct in the Early Permian, the Adelophthalmidae is the longest lasting single family of eurypterids. The survival of the group, and of swimming eurypterids (the suborder Eurypterina) beyond the Late Devonian is entirely due to the survival, and subsequent success, of Adelophthalmus throughout the Devonian and Carboniferous. Adelophthalmus (and possibly Unionopterus) represents the only known genus of swimming eurypterids beyond the extinction of the rest of the group in the Late Devonian, extending the temporal range of the group by over a hundred million years.