See text Mecistocephalidae is a monophyletic family of centipedes in the order Geophilomorpha.

[4] Species of this family are characterized by an elongated head with lateral margins converging backwards; first maxillae with relatively elongate coxosternite, and coxal projections much wider than telopodites, both ending with a distinctly hyaline part; second maxillae with small simple claws; elongate forcipular coxosternite with pleurites projecting anteriorly into scapular points and displaced dorsally so that the coxopleural sutures run anteriorly on the dorsal side; metatergites of the posterior part of the trunk distinctly longer than those on the anterior part.

[1] This family differs from all other geophilomorphs insofar as the number of segments in mecistocephalids is generally fixed within each species and the same for each sex.

[7][4] The family includes centipedes with odd numbers of leg-bearing segments ranging from as few as 41 to as many as 101.

[9][4] The next most common numbers are 45 leg pairs, found in most species in the genus Tygarrup[6] as well as in species distributed among five other genera, and 41 leg pairs, found in all species in the genera Agnostrup, Anarrup, Arrup, Nannarrup, and Partygarrupius as well as in two species of Dicellophilus;[10] fewer mecistocephalid species have 47 leg pairs (e.g., Mecistocephalus angusticeps and M. tahitiensis) or 51 leg pairs (e.g., M. evansi and M. lifuensis),[4][11] found only in the genus Mecistocephalus,[9] and the other remaining numbers are even more rare (e.g., 43 leg pairs, found in Dicellophilus carniolensis[10]).