CHAPTER 16 DIPLOPODA — TAXONOMIC OVERVIEW BY HENRIK ENGHOFF, SERGEI GOLOVATCH, MEGAN SHORT, PAVEL STOEV AND THOMAS WESENER There is no widely accepted consensus about the classification of Diplopoda. The following account basically follows the arrangement by Shear (2011), deviations from this are specified. All currently recognized families are mentioned, and more or less exact numbers of known genera and species in each family are given, as well as the known geographical distribution. With more than 1800 recognized genera (1868 according to Shear, 2011) mentioning and characterizing them all would require a volume in itself. In the following treatment, which is exhaustive down to the families, all genera are mentioned only for some, mainly smaller orders, whereas only a selection of genera are mentioned for the large orders Polydesmida, Chordeumatida, Julida and Spirostreptida. Likewise, the amount of morphological detail varies greatly between orders, and this chapter cannot in general be used as an identification manual. For those genera which are listed, the (approximate) number of known species and the geographical distribution are given, and as a rule the name of at least one species per listed genus is included. Information on habits is included to a limited extent, e.g., if the members of the family/genus are cavernicolous. Only Recent taxa are treated here. For fossils see Chapter 14. Class DIPLOPODA de Blainville in Gervais, 1844 [HENRIK ENGHOFF] Terrestrial mandibulate and tracheate arthropods with adult body size 1.4-350 mm. Cuticle rarely soft and covered by modified setae (Polyxenida), usually calcified, form- ing an inflexible, rarely flexible (Glomeridesmida and Polyzoniida), exoskeleton. Body consisting of head, trunk and telson. Head rarely with (Polyxenida), usually without tri- chobothria. Labrum rarely free (Polyxenida) mostly fused to clypeus, with one (Penta- zonia) or three (Eugnatha) teeth. Ommatidia usually present, few or many (up to 100 © Koninklijke Brill NV, Leiden, 2015 Myriapoda 2 (16): 363-453 364 H. ENGHOFF ET AL. per eye), but some orders (Glomeridesmida, Platydesmida, Siphonophorida, Polydesmida) and families entirely blind, and ommatidia lost in many subterranean species. Organ of Tömösváry present as a small pit, rarely larger (Glomeridesmida, Glomerida), sometimes absent (Colobognatha, Stemmiulida, Juliformia). Antennae with six, seven or eight an- tennomeres, with or without (Polyxenida only) an apical disc carrying generally four, in a few genera more, apical cones. Various sensilla, including sensilla basiconica, usually present on antennomeres, especially dorsally at fifth and sixth (or sixth and seventh in those with eight antennomeres). Epipharynx loosely attached (Pentazonia) or fixed to head capsule (Helminthomorpha). Mandible with one or two (Eugnatha) basal articles and a gnathal lobe. Gnathochilarium variable, order specific, but always consisting of a single, variably subdivided, unpaired plate. Palps of gnathochilarium usually short. Trunk with 9-192 diplosegments (referred to as segments), 11-375 leg pairs. Diplosegments consist- ing of tergite and (fused or associated) two pleurites, four stigmatic plates, two sternites and two pairs of legs. Sternites, stigmatic plates, pleurites and tergites ranging from free to forming a completely fused ring with barely visible sutures. First segment (collum) legless (except Spirobolida), lacking ventral elements. Anterior segments 2-4 (Spirobol- ida: 2-5) each with one associated leg pair. Legs consisting of six (coxa, prefemur, femur, postfemur, tibia, tarsus), rarely seven (coxa, trochanter, prefemur, femur, postfemur, tibia, tarsus) or eight (coxa, trochanter, prefemur, femur, postfemur, tibia, tarsus 1, tarsus 2) podomeres. Coxal pores present or absent. Gonopores opening directly through second coxae, or through a pouch just behind leg pair 2, rarely (Stemmiulida) anteriorly of leg pair 3. Mainly terrestrial decomposers, only a handful of species secondarily adapted to an aquatic lifestyle. Very few species semi-carnivorous (some Callipodida, few Chordeu- matida). Many troglobionts in almost every order. Development by anamorphosis, juveniles hatching with 3, rarely 4 (Colobognatha) exceptionally (Pachyiulus spp.) more than 20 leg pairs. 16 orders with 140 families and more than 11 000 species. Numerous species still awaiting assignment to currently valid families and genera are not listed below. Subclass PENICILLATA Latreille, 1831 [MEGAN SHORT] Order Polyxenida Verhoeff, 1934 Body length usually 1.5-4 mm, more rarely up to 6 mm. Cuticle soft, not calcified. Head covered in rows of trichomes with large number anteriorly and one or more rows posteriorly on the vertex. Posterior margin of head with 3 + 3 trichobothria. Labrum flexible. Ommatidia often present (11 or less in clusters each side), but absent in Lophoproctidae and in a small number of species in Polyxenidae. Organ of Tömösváry a small, round, circular pit located posterior to the antennal base each side. Antennae with eight segments, lacking a disc. Antennomere 8 with four apical sensory cones,.