INVERTEBRATE ZOOLOGY - H. J. 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 CHELICERATES (CHELICERATA)

SUPERCLASS ARACHNIDS (ARACHNIDA)

CLASS PSEUDOSCORPIONS (PSEUDOSCORPIONES)

Pseudoscorpions are widespread, small (2–3 mm, occasionally up to 7 mm) predatory arachnids that lead a secretive lifestyle in soil humus, under stones, beneath tree bark, among leaf litter, in the burrows and nests of vertebrates, and in caves. Some species are synanthropic. Approximately

1.3 thousand species have been described, the majority from tropical regions. In Ukraine, pseudoscorpions have not been the subject of dedicated study. The cosmopolitan common pseudoscorpion, or book pseudoscorpion (Chelifer cancroides), is distributed across the entire territory (Fig. 292, b). Two species from the caves of Crimea and two species from Transcarpathia are also known.

Anatomy and Morphology. The cephalothorax in pseudoscorpions is covered by a carapace, the anterior margin of which bears one to two pairs of eyes, though eyes are sometimes absent. The abdomen is broad and segmented. The chelicerae are small, with pincers featuring comb-like outgrowths. The ducts of paired silk glands, located in the cephalothorax, open at the tips of the movable fingers of the chelicerae. The pedipalps, much like those in scorpions, terminate in pincers used by pseudoscorpions to seize prey. In addition to their grasping function, the pedipalps serve as Organs of Touch, bearing long, sensitive hairs known as trichobothria on their pincers. In many species, the ducts of venom glands open on the pedipalp pincers, and their venom paralyzes the prey. Some species grind their food using the chelicerae, but the majority puncture the victim's body to inject digestive juices before sucking out the liquefied Tissues. Pseudoscorpions prey on small crustaceans, insects, mites, nematodes, and other microfauna.

Pseudoscorpions breathe through tracheae that open on the second and third abdominal segments. Each stigma leads internally to a short tube bearing a bundle of unbranched, long, slender tracheae.

Reproduction. Fertilization is spermatophore-mediated, similar to that in scorpions. Fertilized eggs are deposited into a specialized brood chamber—a distinctive sac-like outpocketing of the genital ducts. The embryos attach to the chamber wall and feed on an Abundance of yolk supplied by the Ovary. They develop into sac-like larvae that remain anchored to the chamber by the mouthparts of the cephalothorax and continue to feed on yolk. Upon molting, the sac-like larva transforms into a protonymph. The protonymph leaves the maternal body and the nest inhabited by the female, and begins actively foraging for food. Three subsequent molts follow, producing the deutonymph, the tritonymph, and the adult, respectively. The genital apparatus of pseudoscorpions forms during the final molt.

Among synanthropic species, the aforementioned book pseudoscorpion is widely known. It inhabits books, linens, and wallpapered walls, feeding primarily on grain mites, booklouse larvae, and similar pests. By destroying these animals, the book pseudoscorpion performs a beneficial service for humans. Another well-known species is Cheiridium museorum, which is frequently found alongside the former species in insect collections and herbariums.

Pseudoscorpions are characterized by The phenomenon of phoresy (dispersal over long distances by attaching to the bodies of other animals).