INVERTEBRATE ZOOLOGY - G. I. Shcherbak - 2008

KINGDOM METAZOA

SUBKINGDOM EUMETAZOA

SECTION TRIPLOBLASTICA, OR BILATERIA

SUBSECTION ECDYSOZOA

PHYLUM ARTHROPODA

SUBPHYLUM TRACHEATA

SUPERCLASS HEXAPODA

CLASS ENTOGNATHA

Small animals inhabiting primarily soils, leaf litter, and less frequently, the herbaceous layer. About 11,000 species have been described, although this group remains insufficiently studied.

Morphology. The HEAD is solid, enclosed in a cuticular capsule into which the mouthparts are retracted. The lateral walls of the Oral Cavity fuse with the lower lip, forming a deep pouch that houses the mandibles and maxillae, with only their tips exposed externally. The head bears a pair of antennae and may feature simple eyes. The thoracic segments are typically free (fused only in some springtails), each carrying a pair of legs. The leg, as in insects, consists of a coxa, trochanter, Femur, Tibia, and tarsus. In some Entognatha, the tibia is fused with the tarsus. The abdomen comprises 11–12 segments, occasionally six (in springtails). Modified or vestigial appendages persist on the abdomen.

The protocerebrum is positioned dorsal to the deutocerebrum. The tracheae are poorly developed or frequently absent entirely, in which case Respiration occurs across the entire body surface.

Development is direct, without metamorphosis. Growth is accompanied by numerous molts.

The Class Entognatha includes three orders.

Order Protura. Minute animals, up to several millimeters in length, inhabiting soil, litter, or rotting wood. 300 species are known.

The body consists of a head and a trunk that is indistinctly divided into Thorax and abdomen (Fig. 355). Eyes and antennae are absent. The mouthparts are modified into elongated piercing-sucking setae. The anterior pair of legs is directed forward and Functions as a tactile organ, while the two posterior pairs are walking legs. The abdomen consists of 12 segments. The first three segments bear paired one- or two-segmented appendages—underdeveloped abdominal legs that support the abdomen during locomotion. They feed on organic debris.

Fig. 355. Protura: Eosentomon transitorum (after Gilyarov)

Order Collembola (springtails). Comprises up to 10,000 species, with many new ones described by scientists every year.

Body dimensions are on the millimeter scale. The head bears simple eyes and four- to six-segmented antennae. Mouthparts are biting or piercing-sucking. Near the Base of the antennae lies a specialized postantennal organ equipped with olfactory and humidity receptors.

The abdomen is six-segmented. The fourth segment features a segmented springing fork (furcula) bent underneath the abdomen and anchored by an appendage of the third segment—the tenaculum (Fig. 356). During a jump, the fork releases from the tenaculum and pushes off the substrate, propelling the body upward. The first abdominal segment bears a specialized appendage, the ventral tube, which secretes a sticky substance that anchors the body upon landing. Some springtails can jump distances of up to 1 m.

Fig. 356. Collembola: a – Entomobrya pulchella; b – Sminthurus viridis (after Dogiel)

Springtails inhabit the soil and its surface, feeding on plant residues, soil Fungi, and Algae. They play a vital role in pedogenesis by facilitating the decomposition of PLANT AND ANIMAL remains. The concentration of certain species in the soil can reach several thousand individuals per 1 m². At the same time, certain species—such as the mushroom-infesting springtail *Ceratorhysella denticulata* (often referred to in regional literature as *Ceratorhysella annata*) common in Ukraine—can damage cultivated mushroom mycelium in greenhouses, while species living on plants occasionally harm garden crops, for instance, the cosmopolitan lucerne flea (*Sminthurus viridis*). Jumping springtails (*Podura aquatica*) occur in masses On the surface of freshwater bodies.

Order Diplura. Approximately 400 species have been described. Body length ranges from 1 mm to 5 cm. The body is elongated, the head bears long segmented antennae, mouthparts are of the chewing type, and eyes are absent (Fig. 357). All legs are structurally similar. The abdomen consists of 11 segments, the first seven of which bear vestiges of abdominal appendages—unsegmented paired styli. The tip of the abdomen bears a pair of appendages, the cerci; in some species (genus *Campodea*) they are filiform and segmented, functioning as tactile Organs, whereas in others (genus *Japyx*) they are shortened, unsegmented, pincer-like, and adapted for capturing prey such as springtails.

Fig. 357. Diplurans: a — Campodea phisiochaeta; b — Japyx confusus (from Dogiel)

Diplurans inhabit soil, decaying wood, ant nests, under stones, etc. Predators prey on small soil-dwelling insects, mites, nematodes, and other invertebrates. They are mainly distributed in regions with warm climates. The species Campodea staphylinus, reaching a length of 1 cm, is known in Ukraine, while Japyx ghilarovi is endemic to the Southern Coast of Crimea.