Instead, propulsion was likely generated by the sixth pair of appendages, the swimming legs used by other eurypterine eurypterids. Whilst stiff dorsally, fossil evidence suggests that "Slimonia" was very flexible laterally (side to side). A specimen of "Slimonia acuminata" from the Patrick Burn Formation of Scotland preserves a complete and atriculated series of telsonal, postabdominal and preabdominal segments. In the specimen, the "tail" is bent to a considerable degree previously unseen in any eurypterid. Capable of bending its tail from side to side, it has been theorised that the tail may have been used as a weapon. The telson spine, serrated along the sides and exceeding the flattened telson in length, ends in a sharp tip and would likely have been capable of piercing prey. In pterygotids, it is likely that the cheliceral claws came to replace telson spikes as weaponry as the telson spikes of that family are relatively shorter than those of the Slimonidae. However, this theory has been proven to be erroneous as the fossil specimen in question was a molt, rather than an actual carcass, and did show apparent signs of disarticulation. The telson of "Salteropterus" is very distinctive and though its function remains unknown (possibly used for additional balancing), it was likely not used as a weapon in the same way the telson of "Slimonia" was. The flattened portion is trigonal and smaller than that of "Slimonia" but the telson spike is far longer, forming something akin to a stem with knobs running alongside it and ending in a tri-lobed organ unseen in any other eurypterid. Slimonid eurypterids are classified as part of the Pterygotioidea superfamily, within the Diploperculata infraorder and Eurypterina suborder. The Slimonidae is often interpreted as a sister-taxon (the most closely related group) to the Pterygotidae. The other Pterygotioid family, the Hughmilleriidae, has also been interpreted as the most closely related sister-taxon to the pterygotids. The discovery of "Ciurcopterus", currently the most primitive known pterygotid, allowed researchers to study its features which showed that the primitive pterygotid combined characteristics of more derived members of its own family and "Slimonia".