"eysyslopterus" is considered to be the most basal adelophthalmid genus due to the position of its eyes. these are placed closer to the margin than to the ocelli, in contrast to any other adelopthalmid. in fact, the carapace of "eysyslopterus" and other basal genera belonging to superfamilies, "orcanopterus" and "herefordopterus", were almost identical. in the waeringopteroid "orcanopterus", the eyes were separated from the margin by the marginal rim, whereas in "herefordopterus" they were completely marginal, a feature present in all pterygotioid genera. in addition, the triangular anterior carapace margin present in "eysyslopterus" was shared with "hughmilleria", indicating that it might be a plesiomorphic trait (a trait present in a common ancestor). these characteristics have led some authors to question whether "eysyslopterus" really represents an adelophthalmid or the sister taxon of a group formed by pterygotioidea and adelophthalmoidea, but until more fossil material is found this can not be proven.