Adelophthalmidae

Adelophthalmidae Temporal range: Late Ordovician-Artinskian, 455–283.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Fossil of Adelophthalmus mansfieldi.
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Order:	†Eurypterida
Suborder:	†Eurypterina
Infraorder:	†Diploperculata
Superfamily:	†Adelophthalmoidea Tollerton, 1989
Family:	†Adelophthalmidae Tollerton, 1989
Type species
†Adelophthalmus granosus Jordan in Jordan & von Meyer, 1854
Genera
†Adelophthalmus †Archopterus †Bassipterus †Eysyslopterus †Nanahughmilleria †Parahughmilleria †Pittsfordipterus †Pruemopterus †Unionopterus? †Wiedopterus?
Synonyms
Nanahughmilleridae Tetlie, 2004 Parahughmilleriidae Plotnick, 1983

Adelophthalmidae (the name deriving from the type genus Adelophthalmus, meaning "no obvious eyes") is a family of eurypterids, an extinct group of aquatic arthropods. Adelophthalmidae is the only family classified as part of the superfamily Adelophthalmoidea, which in turn is classified within the infraorder Diploperculata in the suborder Eurypterina.

Adelophthalmid 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.

Though the last swimming eurypterids and the final members of the traditionally more successful and numerous suborder Eurypterina, the adelophthalmids were not the last eurypterids. The stylonurines or the "walking eurypterids" were the last ones, surviving in the family Hibbertopteridae until the Permian–Triassic extinction event or shortly before a few million years after the extinction of the adelophthalmids in the Early Permian.