INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM MULTICELLULAR ANIMALS (METAZOA)

SUBKINGDOM TRUE METAZOA (EUMETAZOA)

SECTION TRIPLOBLASTIC (TRIPLOBLASTICA) OR BILATERAL (BILATERIA) ANIMALS

SUBSECTION MOLTING ANIMALS (ECDYSOZOA)

PHYLUM ARTHROPODS (ARTHROPODA)

SUBPHYLUM CHELICERATES (CHELICERATA)

SUPERCLASS ARACHNIDS (ARACHNIDA)

CLASS SPIDERS (ARANEAE)

Spiders have successfully colonized terrestrial habitats ranging from temperate zones and high mountains to arid steppes and scorching deserts. They inhabit the soil, where they dig burrows or occupy natural crevices, as well as leaf litter, moss, grass, caves, burrows and nests of other animals, human dwellings and outbuildings, the littoral zone (the intertidal area of seashores exposed during low tide), and freshwater margins. However, only a single species is truly aquatic: the Water spider (Argyroneta aquatica), which breathes air stored inside a submerged web nest it constructs underwater. About 35,000 spider species have been described, with over 2,000 species recorded in Ukraine.

Body length (excluding legs) ranges from 0.8 mm to 11 cm. Many species are brightly colored, often featuring complex patterns.

Anatomy and Morphology. The spider's body consists of a cephalothorax covered by a hard dorsal shield and connected by a narrow pedicel to an unsegmented (in the vast majority of species) abdomen (Fig. 301). Eight eyes are situated on the anterior part of the cephalothorax. Vision varies functionally among different spider groups: in some, the eyes merely perceive light intensity and direction while detecting the movement of various objects, whereas others possess form vision. Jumping spiders actively track prey with their eyes, which are moved by specialized Muscles.

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Fig. 301. Female European garden spider (after Ivanov): a - dorsal view; b - cephalothorax; c - ventral view of the abdomen:

1 - pedipalps; 2 - chelicerae; 3 - cephalothorax; 4 - sclerotized cuticular areas; 5 - abdomen; 6 - walking legs; 7 - terminal claw-like segment of the chelicera; 8 - gnathobases (maxillary lobes) of the pedipalp coxae; 9 - coxae of the second walking legs; 10 - attachment site of the pedicel; 11 - book lung opercula; 12 - stigma of the right lung; 13 - tracheal spiracle; 14 - spinnerets; 15 - anal tubercle

The chelicerae are relatively small and two-segmented,

consisting of a basal segment and a fang through which the duct of the poison gland opens. Spiders use their chelicerae to capture and kill prey, tear it apart when necessary, dig soil, and carry egg cocoons; occasionally, males use them to hold females during courtship. The pedipalps are leg-like appendages whose coxae are expanded into masticatory lobes that bound the preoral cavity, while their covering hairs serve to strain food. The primary function of the pedipalps is sensory. In males, the terminal segments of the pedipalps are modified into copulatory Organs (Fig. 302). The legs are multifunctional, serving for locomotion, burrowing, holding prey, and carrying egg cocoons. Using its legs, a spider spins, grooms, and tears spider silk. The entire body and legs of spiders are covered with numerous hairs and setae, some of which function as mechano- and chemoreceptive sensilla.

Fig. 302. Diagram of a spider's copulatory organ (after Dogiel):

1 - alveolus; 2 - spermatophore opening; 3 - spermatophore;

4, 5 - upper and lower folded PARTS OF THE copulatory organ, respectively; 6 - modified tarsus of the pedipalp

On the ventral side, near the anterior end of the abdomen, lies the genital opening, flanked by the openings of the pulmonary sacs (book Lungs). Further posteriorly are two to three pairs of spinnerets (Fig. 303) covered with numerous (up to 600) short tubules, at the tips of which open the ducts of silk glands. Their secretion hardens rapidly upon contact with air, forming silk threads.

Fig. 303. Spinning apparatus of the European garden spider (after Lange):

a - tip of the leg tarsus; b - external appearance of the spinnerets;

c — individual silk tubule; 1, 2 — paired and unpaired pectinate claws, respectively; 3 — serrated spines;

4 — setae; 5, 6 — external and internal spinnerets, respectively; 7 — anal tubercle

Silk plays an exceptionally important role in the life of spiders: it is used to construct trapping webs, wrap prey before Digestion, line the walls of burrows and doors sealing the burrow entrance, provide material for egg cocoons, and facilitate the aerial dispersal of juveniles, among other Functions. This versatility is due to the Different types of silk produced (dry, wet, corrugated, adhesive, etc.). In its Chemical Composition and physical properties, spider silk is very similar to silkworm silk, but it is significantly more elastic and stronger. Undoubtedly, the evolution of silk glands was a prerequisite for the Progressive development of this animal group.

All spiders are voracious predators, feeding primarily on insects, which they liquefy and consume by sucking. Their Digestive System features specific adaptations for this feeding mechanism: the posterior section of the Esophagus expands into a muscular sucking Stomach, while the midgut in the cephalothorax forms five pairs of blind diverticula, allowing spiders to ingest large amounts of liquid food. Spiders employ various hunting strategies: ambushing prey, actively hunting (with wandering forms entangling prey in silk), or utilizing various trapping devices—ranging from simple signal threads to complex webs.

The respiratory organs in spiders consist of book lungs (tetrapulmonate spiders), book lungs and tracheae (dipulmonate spiders), or tracheae alone (in some tropical species).

Reproduction. Spiders exhibit pronounced Sexual Dimorphism. As a rule, males are smaller than females, sometimes even dwarfed, and possess brighter coloration, specialized shapes of certain leg pairs, etc. Spermatophores are absent; prior to mating, the male spins a small web upon which he releases a drop of seminal fluid. He then loads this fluid into his copulatory organs (the terminal segments of the pedipalps) and actively searches for a female using his SENSE OF SMELL. Mating is sometimes preceded by characteristic prolonged courtship displays, as well as male-male combat for the female. Fertilized eggs are deposited in silk cocoons and are frequently guarded by the female until the young hatch.

The ecological impact of spiders has not been fully studied, but it is evident that by destroying significant numbers of agricultural and forestry insect pests, they play a beneficial role. However, spiders whose venom affects warm-blooded animals and humans are more widely known; the venom of some species has only a local effect, causing necrosis and tissue destruction at the bite site, while the venom of others affects the entire Organism, particularly The Nervous system. Large spiders (up to 10 cm) of the family Aviculariidae—commonly known as tarantulas—are frequently kept in captivity. Most of them are harmless to humans, though some possess venom that can be fatal.

In Ukraine, the two best-known venomous spider species are the South Russian tarantula (Lycosa singonensis), found in the steppe and forest-steppe zones as well as Crimea, and the Mediterranean black widow. The tarantula has a yellowish-brown body 3–4 cm in length, a rounded-triangular cephalothorax, and an elongated oval abdomen; its bite causes only local inflammation in humans. The other species, the karakurt (Latrodectus tredecimguttatus), occurs in Crimea and certain areas of the steppe zone; its venom affects the entire human body. Karakurt spiders are small in size (females 10–20 mm, males 4–7 mm) and black in color, with males and juveniles of both sexes bearing red spots on the abdomen (Fig. 292, d). Sexually mature females are the most dangerous. Livestock suffer greatly from karakurt bites, with camels and horses being particularly sensitive and frequently dying. In the Americas, a similarly venomous species of the same genus, L. mactans, commonly known as the "black widow," is widespread.