INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE MULTICELLULAR ANIMALS (EUMETAZOA)

DIVISION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBDIVISION MOLTING ANIMALS (ECDYSOZOA)

PHYLUM ARTHROPODS (ARTHROPODA)

SUBPHYLUM TRACHEATES (TRACHEATA)

SUPERCLASS MYRIAPODS (MYRIAPODA)

CLASS MILLIPEDES (DIPLOPODA)

The largest Class of myriapods. Over 8,000 species have been described, though some estimates suggest there are at least 50,000. Most of them inhabit the tropical and subtropical Zones of the Earth, occupying the upper layers of humus-rich soil, decaying plant debris, and rotting wood. More than 120 species have been found in Ukraine; one species, Leptojulus semenkevitshi, and one subspecies, Polydesmus montanus ukrainicus, are listed in the Red Data Book of Ukraine.

Sizes range from a few millimeters, as in Polyxenus lagurus, to 28 cm (in the tropical species Craplidostreptus gigas). The body is typically elongated, rarely shortened. Diplopods, especially tropical forms, often feature bright coloration.

Morphology. The body consists of a HEAD (which possesses one segment fewer than in other myriapods), a free legless cervical segment, and a multi-segmented trunk (Fig. 349). The antennae are short, most commonly eight-segmented. Situated behind the upper lip and a pair of robust, toothed mandibles is a single unpaired plate—the gnathochilarium—formed by the fusion of the first pair of maxillae. The gnathochilarium Functions as a lower lip, supporting food near the Mouth. The eyes consist of clusters of simple ocelli, or are sometimes entirely absent.

Fig. 349. Millipedes (from Ivanov):

a - structural diagram of an julid millipede; b - head in ventral view; c - Mandible; d - gnathochilarium:

1 - antenna; 2 - cluster of simple ocelli; 3 - head; 4 - dorsal shield of the first "legless" segment; 5 - segments with a single pair of legs; 6 - segments with two pairs of legs; 7 - openings of poison glands; 8 - young "legless" segments; 9 - telson; 10 - anal valve lobe; 11 - unpaired subanal plate; 12 - trunk appendages; 13 - gonopod; 14 - Location OF THE genital aperture;

15 - modified appendages of the second segment; 16 - cheek; 17 - mandible; 18 - labrum; 19 - gnathochilarium

The trunk comprises three anterior segments bearing a single pair of appendages each, followed by doubled segments—diplosegments—with two pairs of legs on each, and terminates in a telson, which may bear setae, spinneret styles (warts), and the like. Anterior to the telson lies the zone of new segment formation, which always contains several incompletely formed legless segments. Males possess modified reproductive

legs—gonopods—on the first and eighth trunk segments. In adult diplopods, the number of segments ranges from 11 to 170.

When disturbed, most millipedes curl into a ball, protecting their head and appendages with sturdy dorsal shields (the ventral side is always significantly less sclerotized).

The integument is typically impregnated with calcium carbonate, making it very tough and rich in unicellular and multicellular cutaneous glands, among which defensive glands are of particular interest. They eject a caustic secretion that in some species (e.g., the tropical Fontana) contains hydrocyanic acid and smells of bitter almonds, while in others it has the scent and burning taste of camphor. In many diplopods, disturbance causes the poison to be released as a droplet, whereas in some it is forcefully sprayed up to 75 cm to either side, as seen in the Tahitian species Rinocrinus salvo and certain julid millipedes.

The Digestive System, like that of other myriapods, resembles a straight tube; the excretory system, similar to that of centipedes, is represented by a pair of Malpighian tubules. The fat body performs the function of excreta storage.

The Circulatory system is similar to that of centipedes, but lacks a ventral vessel. In the first four segments, The Heart chambers possess one pair of ostia each, while all other chambers have two pairs.

The tracheal system begins with a pair of spiracles located at the Base of the legs on each segment, except for the few anterior ones. Each spiracle leads to a pouch-like dilation from which more or less branched tracheae extend, supplying oxygen to the Organs of the respective segment. Unlike centipedes and insects, diplopods do not form a unified tracheal system.

The Nervous system is typical of tracheates. Its structural peculiarity lies in the fact that the ventral nerve cord contains a single paired ganglion in the cervical and first three trunk segments, but two pairs per diplosegment.

Sense Organs. On the sides of the head in many diplopods, there are clusters of simple ocelli, although blind species also exist. Numerous spine-like and club-shaped sensilla are located on the antennae and gnathochilarium, which presumably function as chemoreceptors. In many diplopods, on the sides of the head between the antennae and ocelli, lie the so-called Tömösváry organs—pits containing sensory Cells, which are likely auditory or olfactory organs. Tactile functions are performed by sensory setae scattered across the antennae, trunk, and legs.

Reproductive System. The female and male Gonads are unpaired, appearing as elongated sacs that continue into an unpaired duct (oviduct or sperm duct) which then bifurcates and opens throu

gh a pair of openings on the third trunk segment, unlike centipedes and insects, where the genital openings are always located on the posterior segments.

Reproduction. Fertilization is spermatophoric. Development proceeds via anamphibious-like anamphibosis (anamorphosis): a larva hatches from the egg with three leg-bearing segments and several legless ones (Fig. 350). During subsequent molts, legs appear on the previously legless segments, and new legless segments form anterior to the telson, a process that continues throughout life. In some diplopod species, notably the millipede Ommatojulus sabulosus, a phenomenon unique to the animal world known as periodomorphosis has been discovered—namely, the ability of adult males to revert to a juvenile (larval) form after a subsequent molt. This leads to The formation of so-called "intercalary males." This extends the overall lifespan of such individuals by 1.5 to 2 times and is believed to ensure population survival under adverse conditions.

Fig. 350. Six-legged larva of a millipede (from Dogiel): 1 - telson; 2 - head; 3 - antenna; 4 - leg buds; 5 - leg

Diplopods can be conditionally divided into two groups. One includes small (2–4 mm) animals with soft integuments, united in the order Polyxenida (Fig. 351); the second includes the so-called millipedes (in reality, they have significantly fewer legs—for instance, one of the largest diplopods, the Seychelles millipede, possesses 175 trunk segments but only 139 pairs of legs). The second group is characterized by robust integuments rich in calcium carbonate. There is A large number of millipede orders (over 10), with the most common being Representatives of the orders Julida, Polydesmida, and Glomerida (Fig. 352).

Fig. 351. Bristle millipede Polyxenus lagurus (from Crome)

Fig. 352. Millipedes (Diplopoda):

a - pill millipede Glomeris marginata (from Crome); b - polydesmid Strongylosoma stigmatosum; c - millipede Rhinocrinus sp. (from Gilyarov)

One of the best-known and most thoroughly studied groups of millipedes is the order Julida. Their body is cylindrical, with a large number (at least 30) of trunk segments. They move slowly across open surfaces, with the Muscle contractions of the legs propagating in a wave-like manner from front to back. They also easily burrow into leaf litter and soil, penetrating deeper when the surface layers dry out.

Millipedes inhabit leaf litter and other decomposing organic matter; some permanently dwell in the soil or beneath the bark of trees and rotting stumps. Many species settle in cultivated areas and greenhouses. The European species Archiboreojulus pallidus, which is also widespread in Ukraine, has become a dangerous pest of vegetable crops in gardens and greenhouses, reaching densities of over 1500 individuals/m². In tropical regions, large millipedes are used for food.

Representatives of the order Glomerida (also known as pill millipedes) externally resemble woodlice. They have a short body with wide, hard tergites; their integument is glossy, bare, and vividly patterned. Their length reaches up to 10 mm with a width of 5 mm. Glomerids are strictly hygrophilous; to protect against desiccation, they possess The ability to roll up into a tight sphere and remain in this state for hours or even days. The most common species in Ukraine, Glomerula hexasticha, is a typical inhabitant of hornbeam forests.

Diplopods are primarily saprophages, although predators and species with a sucking proboscis also occur among them. They play a significant role as primary decomposers of dead plant material in maintaining

natural soil fertility. Some species are facultative phytophages and may damage the roots of cultivated plants, seedlings, and seeds, or spoil berries. Despite the presence of poison glands and a cryptic lifestyle, diplopods are readily consumed by amphibians and birds, especially starlings.