Two-legged

Diplopods have an elongated body, from a few millimeters to 10-20 cm long. It consists of a head, a free cervical segment and a segmented trunk.

The diplopod head consists of a fused acron and three head segments, and the fourth head segment is free (cervical). On the head of diplopods there are antennas - acronis appendages and two pairs of jaws: mandibles (limbs of the second segment) and gnatochilaria - an unpaired plate formed as a result of the fusion of the first pair of maxillas (limbs of the third segment). Gnatohilaria performs the function of the lower lip - supports food at the mouth. From above, the mouth parts are covered with a skin fold - the upper lip. The first segment of the head - intercalary (insertion) - does not carry appendages. The cervical segment is also without limbs. It forms a cranked bend between the body and the head perpendicular to it. On the head, on the sides of the antennae, there are simple, or false-faceted, eyes consisting of a cluster of simple eyes. Some species are blind.

The trunk of the diplopod is divided into two parts. The front consists of three segments, bearing one pair of legs. The second includes all subsequent double segments (diplosomites), each of which has two pairs of legs. The trunk ends with the anal lobe - telson . The male has modified genital legs - gonopods on the first and eighth trunk segments. The number of trunk segments in diplopods is not less than 30 and can reach 75, and the number of leg pairs is 139. The Illacme plenipes Cook & Loomis (California; Siphonophorida : Siphonorhinidae) species has a record number of legs - up to 750 (375 pairs of legs) ^[2] .

The formation of diplosomites is a special way of arthropod oligomerization, in which segments merged in the process of evolution in pairs without the formation of tags .

Despite the large number of legs, diplopods move slowly. Due to their low mobility, they have protective morphological and ethological devices. A hard chitinous coat saturated with calcium carbonate protects their body from predators, mechanical damage and from drying out. Like many burrowing soil animals, the body of bipedal centipedes is often round in diameter. This allows them to bury in the soil litter and in the upper soil layer. In case of danger, they curl up into a ring or spiral, covering the vulnerable abdominal surface of the body.

Another protective device of these organisms is the odorous glands, the openings of which are located on each diplosomite. Their secretions are often toxic, in some species they contain hydrocyanic acid. For many animals, kivsyaki is inedible. In mammals, odorous secretions can irritate the mucous membranes of the eyes and nasopharynx, but diplopods are readily eaten by reptiles and birds . Some types of diplopods have warning colors with bright stripes, and the pungent smell has the meaning of a warning signal.

The digestive system of the diplopod consists of three sections and has the shape of a rectal intestinal tube. Three pairs of salivary glands of mesodermal origin fall into the oral cavity, which gives reason to consider them derivatives of whole foods . The narrow esophagus passes into the large intestine. The hind gut is long and is divided into several sections. Differentiation of the hindgut is associated with the fermentation processes occurring in it, which are also characteristic of other animals that feed on plant debris.

Diplopods have one pair of malpigium vessels , which, like insects , are of ectodermal origin. They flow into the hind gut at the border with the middle, where water is absorbed from excreta into the blood. The function of the kidneys of accumulation is performed by the fatty body, in the cells of which excreta accumulate. This is an additional function of the fat body, which is mainly a spare tissue.

The respiratory system is based on the trachea . In diplopods, on each diplosomite there are two pairs of stigmas (respiratory openings) and one pair - on the first segments of the trunk. The diplopod tracheas are the most primitive in structure: a bundle of trachea departs from each spiracle and is isolated from the others.

The circulatory system has an open structure. The long heart consists of numerous chambers, the number of which corresponds to the number of trunk segments. Each heart chamber in diplosomites has two pairs of ostium openings. Arteries extending from the heart branch many times. Blood poured into the gaps of the mixocell. Blood is collected from the lacunae into the abdominal venous vessel, and from it into the pericardial sinus, then through the ostia it enters the heart again. Special pterygoid muscles are suitable for the heart, contributing to the contractions of the chambers.

The nervous system consists of the brain, periopharyngeal connectivity and the abdominal nerve chain. The brain consists of two departments that innervate the eyes and antennas. The pharyngeal ganglion innervates the oral apparatus. Diplopods in the cervical segment and in the first three trunk segments have one paired ganglion, and two in the diplosomites. The sense organs are poorly developed. There are clusters of simple eyes on the head. In some soil forms, the eyes are reduced. The antennae perform the function of the organs of touch and smell.

Diplopods are dioecious. The gonads are fused into an unpaired gland, from which an unpaired duct (vas deferens or oviduct) departs, which then bifurcates. Paired genital openings are located on the second trunk segment. Fertilization is spermatophore. The male secretes spermatophores, which are picked up by the anterior sexual legs and transmitted by walking legs to the posterior sexual legs on the eighth trunk segment. When mating, the male transfers spermatophores to the female's genital openings.

The type of development inherent in all diplopods is anamorphosis . A larva emerges from an egg with an incomplete set of segments and only three pairs of legs (on segments of the anterior torso). Among diplopods, three types of anamorphic growth are found: euanamorphosis , hemianamorphosis, and bodyanamorphosis ^[3] . Representatives with the first type of development (for example, from the Helminthomorpha subclass) increase the number of segments and legs with each molt even after puberty. In case of hemianamorphosis, after reaching the number of segments of a molt specific for a given species, the number of segments does not increase. Finally, body-anamorphic diplopods do not fade after reaching puberty.

The oldest diplopods were found in deposits of the middle Silurian of Scotland ^[4] . Their spiracles are the oldest surviving organs of terrestrial animals, adapted for breathing by atmospheric air ^[5] .

The class includes about 140 families ^[6] , united in the following taxa of rank ranging from subclass to infraorder inclusive ^[7] :

• † Subclass Arthropleuridea Waterlot, 1934 (1-3 orders, 1-3 families)
• Subclass Penicillata Latrielle, 1831

• Order Polyxenida Lucas, 1840 - The Kisteviki , or the carpal tails , or the polyxenides (2 superfamilies, 4 families)

• Subclass Chilognatha Latrielle, 1802/1803
  • Infraclass Pentazonia Brandt, 1833
    • Squads incertae sedis
      • † Order Zosterogrammida Wilson, 2005
    • Suborder Limacomorpha Pocock, 1894
      • Order Glomeridesmida Cook, 1895 (2 families)
    • Supercat Oniscomorpha Pocock, 1887 - Millipedes- Armadillos
      • Order Glomerida Brandt, 1833 (2 families)
      • Order Sphaerotheriida Brandt, 1833 (4 families)
  • Infraclass Helminthomorpha Pocock, 1887
    • Order Platydesmida Cook, 1895 (2 families)
    • Order Polyzoniida Cook, 1895 (3 families)
    • Order Siphonocryptida Cook, 1895 (1 family)
    • Order Siphonophorida Newport, 1844 (2 families)
    • Suborder Juliformia Attems, 1926
      • Order Julida Brandt, 1833 - Kivsyaki (5 superfamilies, 17 families)
      • Order Spirobolida Cook, 1895
        • Suborder Spirobolidea Cook, 1895 (11 families)
        • Suborder Trigoniulidea Brolemann, 1913 (2 families)
      • Order Spirostreptida Brandt, 1833
        • Suborder Cambalidea Cook, 1895 (5 families)
        • Suborder Spirostreptidea Brandt, 1833 (2 superfamilies, 5 families)
    • Suborder Nematophora Verhoeff, 1913
      • Order Callipodida Pocock, 1894
        • Suborder Callipodidea Pocock, 1894 (1 family)
        • Suborder Schizopetalidea Hoffman, 1973 (5 families)
        • Suborder Sinocallipodidea Shear, 2000 (1 family)
      • Order Chordeumatida Pocock 1894
        • Suborder Chordeumatidea Pocock 1894 (1 superfamily, 2 families)
        • Suborder Craspedosomatidea Cook, 1895 (7 superfamilies, 32 families)
        • Suborder Heterochordeumatidea Shear, 2000 (4 superfamilies, 10 families)
        • Suborder Striariidea Cook, 1896 (2 superfamilies, 5 families)
      • Order Stemmiulida Cook, 1895 (1 family)
      • Order Siphoniulida Cook, 1895 (1 family)
    • Superorder Merochaeta Cook, 1895
      • Order Polydesmida Pocock, 1887 - Multilinks
        • Suborder Leptodesmidea Brolemann, 1916 (5 superfamilies, 13 families)
        • Suborder Dalodesmidea Hoffman, 1980 (2 families)
        • Suborder Strongylosomatidea Brolemann, 1916 (1 family)
        • Suborder Polydesmidea Pocock, 1887
          • Infrastructure Oniscodesmoides Simonsen, 1990 (2 superfamilies, 5 families)
          • Infraorder Polydesmoides Pocock, 1887 (4 superfamilies, 8 families)

• Vials
• Anthroleucosomatidae
• Fagina silvatica

• Sharova I. Kh. Zoology of invertebrates. - M .: Vlados, 2002.
• Brusca RC, Brusca GJ Invertebrates. - second ed. - 2006.

• Golovach S.I. (1980). Two-legged millipedes // Itogi Nauki i Tekhniki. VINITI. Zool. invertebrates. - 1980. - T. 7. - S. 5-62.
• Golovach S.I. (1984). Distribution and faunogenesis of double-legged millipedes of the European part of the USSR // Faunogenesis and filocenogenesis. - M .: Nauka, 1984. - S. 92-138.
• Lokshina I.E. Qualifier of bipodopodic millipedes Diplopoda of the flat part of the European territory of the USSR . - M .: Nauka, 1969 .-- 78 p.
• Mikhaljova EV The millipedes (Diplopoda) of the Asian part of Rossia. Pensoft Series Faunistica. - 2004. - No. 39. - 293 p.