- This New World Vinegaroon from Florida was previously known as Mastigoproctus giganteus and Mastigoproctus giganteus floridanus.
- Carapace dark reddish brown, anterior and lateral margins dark brown. Tergites I–IX dark reddish brown (♂) to reddish brown (♀), posterior and lateral borders darker. Sternites I and II light reddish brown mesally, margins reddish brown; III–IX and pygidium reddish brown (♀) to dark reddish brown (♂). Flagellum light reddish brown, segments with reddish-brown macrosetae. Pedipalp trochanter, femur, patella, and tibia dark reddish brown, mesal surfaces with few reddish macrosetae; patellar apophysis, fixed finger, and basitarsus blackish, with few reddish macrosetae. Legs I–IV reddish brown; II–IV coxae, ventral surfaces light reddish brown.
- Mastigoproctus floridanus most closely resembles M. giganteus, from which it differs as follows: In the adult male of M. floridanus, spines S4 and S5 on the prodorsal margin of the pedipalp trochanter are blunt and a short, blunt subapical accessory spine (AS) is present whereas, in the adult male of M. giganteus, all spines on the prodorsal margin of the pedipalp trochanter are sharply pointed and an AS is absent.
- Mastigoproctus floridanus also differs from M. cinteotl, sp. nov., and M. tohono, sp. nov., as follows. The carapace epistoma is visible in dorsal aspect in M. floridanus but not in M. cinteotl and M. tohono, and the lateral borders of the carapace are almost smooth in M. floridanus but strongly serrate in M. tohono. Spines S4 and S5 on the prodorsal margin of the pedipalp trochanter of the adult male are short and blunt in M. floridanus whereas S4 and S5 are longer and sharply pointed in M. cinteotl, and S4 is shorter in M. tohono.
- Carapace dark reddish brown, anterior and lateral margins dark brown. Tergites I–IX dark reddish brown (♂) to reddish brown (♀), posterior and lateral borders darker. Sternites I and II light reddish brown mesally, margins reddish brown; III–IX and pygidium reddish brown (♀) to dark reddish brown (♂). Flagellum light reddish brown, segments with reddish-brown macrosetae. Pedipalp trochanter, femur, patella, and tibia dark reddish brown, mesal surfaces with few reddish macrosetae; patellar apophysis, fixed finger, and basitarsus blackish, with few reddish macrosetae. Legs I–IV reddish brown; II–IV coxae, ventral surfaces light reddish brown.
- Mastigoproctus floridanus most closely resembles M. giganteus, from which it differs as follows: In the adult male of M. floridanus, spines S4 and S5 on the prodorsal margin of the pedipalp trochanter are blunt and a short, blunt subapical accessory spine (AS) is present whereas, in the adult male of M. giganteus, all spines on the prodorsal margin of the pedipalp trochanter are sharply pointed and an AS is absent.
- Mastigoproctus floridanus also differs from M. cinteotl, sp. nov., and M. tohono, sp. nov., as follows. The carapace epistoma is visible in dorsal aspect in M. floridanus but not in M. cinteotl and M. tohono, and the lateral borders of the carapace are almost smooth in M. floridanus but strongly serrate in M. tohono. Spines S4 and S5 on the prodorsal margin of the pedipalp trochanter of the adult male are short and blunt in M. floridanus whereas S4 and S5 are longer and sharply pointed in M. cinteotl, and S4 is shorter in M. tohono.