Erettopterus is a genus of prehistoric eurypterid. It was related to another large eurypterid, Pterygotus.
Pterygotidae, which lived from the Ordovician to Devonian periods, were characterized by small to large exoskeletons with semilunar scales. The telson, (tail) was expanded, or flatter than it was tall. Pterygotidae also had chelicerae (claws in front of the mouth) that were large and long, with strong, well developed teeth on the claws. Their walking legs were small and slender, without spines.
Erettopterus is distinguishable from other Pterygotidae by its telson, which is bilobed. The distal margins of the chelicerae are angular. The prosoma (head) is semielliptical, with compound eyes located at the edge.
Erettopterus Salter in Huxley & Salter, 1859
Erettopterus bilobus (Salter, 1856) — Silurian, Scotland
= Eurypterus perornatus Salter, 1856 — Silurian, Scotland
= Pterygotus bilobus var. acidens Woodward, 1878 — Silurian, Scotland
= Pterygotus bilobus var. crassus Woodward, 1878 — Silurian, Scotland
= Pterygotus bilobus var. inornatus Woodward, 1878 — Silurian, Scotland
= Pterygotus bilobus var. perornatus Woodward, 1878 — Silurian, Scotland
= Pterygotus perornatus var. plicatissimus Salter in Huxley & Salter, 1859 — Silurian, Scotland
Erettopterus brodiei Kjellesvig-Waering, 1961 — Silurian, England
Erettopterus canadensis (Dawson, 1879) — Silurian, Canada
Erettopterus exophthalmus Kjellesvig-Waering & Leutze, 1966 — Silurian, USA
Erettopterus gigas Salter in Huxley & Salter, 1859 — Silurian, England
Erettopterus globiceps Clarke & Ruedemann, 1912 — Silurian, USA
Erettopterus grandis Pohlman, 1881 — Silurian, USA
Erettopterus holmi (Størmer, 1934) — Silurian, Norway
Erettopterus laticauda Schmidt, 1883 — Silurian, Estonia
Erettopterus marstoni Kjellesvig-Waering, 1961 — Silurian, England
Erettopterus megalodon Kjellesvig-Waering, 1961 — Silurian, England
Erettopterus osiliensis Schmidt, 1883 — Siluria, Estonia,
Erettopterus saetiger Kjellesvig-Waering, 1964 — Silurian, USA
Erettopterus serratus Kjellesvig-Waering, 1961 — Devonian, USA
Erettopterus spatulatus Kjellesvig-Waering, 1961 — Silurian, England
?Erettopterus vogti Størmer, 1934a — Devonian, Norway
Erettopterus waylandsmithi Kjellesvig-Waering & Caster, 1955 — Silurian, USA
