Stylonurid eurypterids (Arthropoda : Chelicerata) include some of the largest known arthropods; bizarre sweep-feeding hibbertopterids from the Carboniferous to end-Permian. New material of Drepanopterus abonensis, a stylonurid from the Late Devonian (Famennian) of Portishead, south-west England, offers key insights into this genus and its affinities. A redescription utilising the new material enables D. abonensis to be assigned as basal member of the Superfamily Hibbertopteroidea, the large-sweep feeding forms, possessing a cleft metastoma and blades (modified blunt spines) on their anterior prosomal appendages. D. abonensis also shares characters such as a clavate telson and median ridge on the carapace with the proposed hibbertopteroid sister-group, the Kokomopteroidea. Hibbertopteroid eurypterids are the most long-ranging stylonurids, surviving the decline and extinction of the other eurypterid families in the Late Devonian, their survival probably due to their sweep-feeding mode of life, which was not in direct competition with their eurypterine relatives and other predators.

Key words: Palaeozoic, Famennian, Drepanopteridae, Sweep-feeding, Old Red Sandstone, Hibbertopteroidea, Palaeoecology.