Eysyslopterus

Eysyslopterus Temporal range: Ludlow, 422.9–418.7 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Restoration of the carapace of E. patteni based on Tetlie and Poschmann's of 2008
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Order:	†Eurypterida
Superfamily:	†Adelophthalmoidea
Family:	†Adelophthalmidae
Genus:	†Eysyslopterus Tetlie & Poschmann, 2008
Type species
†Eysyslopterus patteni Størmer, 1934
Synonyms
Hughmilleria patteni Størmer, 1934 Hughmilleria (Nanahughmilleria) patteni Kjellesvig-Waering, 1961 Nanahughmilleria patteni Kjellesvig-Waering & Leutze, 1966

Eysyslopterus is a genus of eurypterid, an extinct group of aquatic arthropods. Eysyslopterus is classified as part of the family Adelophthalmidae, the only clade within the derived ("advanced") Adelophthalmoidea superfamily of eurypterids. One fossil of the single and type species, E. patteni, has been discovered in deposits of the Late Silurian period (Ludlow epoch) in Saaremaa, Estonia. The genus is named after Eysysla, the Viking name for Saaremaa, and opterus, a traditional suffix for the eurypterid genera, meaning "wing". The species name honors William Patten, an American biologist and zoologist who discovered the only known fossil of Eysyslopterus.

Eysyslopterus is a little-known basal genus that was distinguished from the rest of adelophthalmids by the position near the head margin of the eyes, different from the rest of its relatives. Its carapace was parabolic (approximately U-shaped) and with transverse deep furrows forming the ornamentation. With an estimated length of 8 cm (3.1 in), Eysyslopterus was a small eurypterid. It lived in a nearshore lagoonal quiet community along other eurypterid species.