Modern research favors a classification into suborders Eurypterina and Stylonurina instead, supported by phylogenetic analyses. In particular, pterygotid eurypterids share a number of homologies with derived eurypterine eurypterids such as the adelophthalmids, and are thus best classified as derived members of the same suborder. In the Stylonurina, the sixth pair of appendages is represented by long and slender walking legs and lack a modified spine (referred to as the podomere 7a). In most eurypterids in the Eurypterina, the sixth pair of appendages is broadened into swimming paddles and always has a podomere 7a. 75% of eurypterid species are eurypterines and they represent 99% of all fossil eurypterid specimens. Of all eurypterid clades, the Pterygotioidea is the most species-rich, with over 50 species. The second most species-rich clade is the Adelophthalmoidea, with over 40 species.