These arachnids can reach a length of 18–85 millimetres (0.71–3.35 in). The body consists of a cephalothorax coated with chitin and of an abdomen divided into 12 segments.
The largest of prehistoric whipscorpions and possibly the largest-known whipscorpion ever discovered[3] was Mesoproctus from this family. While M. rowlandi reached 16.8 mm (0.66 in) in length (without tail), an unnamed species M. sp. had a carapace of 32.5 mm (1.28 in) in length and 16 mm (0.63 in) in width, comparable or even larger than the extant Mastigoproctus have.[4]