Mecistocephalidae
Mecistocephalidae are a monophyletic family of centipedes in the order Geophilomorpha. It is the only family in the suborder Placodesmata. 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. Most mecistocephalid species have 49 pairs of legs, but the family includes centipedes with odd numbers of leg pairs ranging from as few as 41 (e.g., the genera "Agnostrup", "Anarrup", "Arrup", "Nannarrup", and "Partygarrupius") to as many as 101. Variation in the number of leg-bearing segments within each sex and within  species has been recorded among the mecistocephalid species with the greatest number of legs: "Mecistocephalus diversisternus", which has 57 or 59 leg pairs, "M. japonicus", which has 63 or 65 leg pairs, and "M. microporus", which has odd numbers of leg pairs ranging from 93 to 101. Genera. The family contains the following genera: Description. Species of the suborder Placodesmata 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.