This family was not assigned to any superfamily due to the poor knowledge of the second to fourth appendages of its only genus, "Alkenopterus". Alkenopteridae was distinguished by the "Drepanopterus"-type B (with no podomere 7a) fifth appendage and an ""Alkenopterus"-type" sixth appendage, this one having podomeres almost equal in length (except the distal spine) and moderately flattened. Both pairs of appendages lacked spines. The "Alkenopterus"-type leg was introduced as a new standard type of non-spiniferous eurypterid appendage. "Alkenopterus" (as well as Drepanopteridae, now monotypic) would be subsequently included in the Stylonurina suborder for not possessing the podomere 7a. However, in 2014, Poschmann reexamined the holotype of "A. burglahrensis" by carefully removing some of the matrix of the fossil and using light microscopy with a higher magnification. This resulted in the detection of a movable podomere 7a instead of a simple projection as previously thought. Therefore, Poschmann assigned it to the family Onychopterellidae, with whom it shared several characteristics. It is assumed that in the fossils of "A. brevitelson", this podomere was not preserved, but if this is not the case, "A. brevitelson" should be reassigned to Stylonurina and "A. burglahrensis" to a new onychopterellid genus.