INVERTEBRATE ZOOLOGY - H. I. Shcherbak - 2008

KINGDOM METAZOA

SUBKINGDOM EUMETAZOA

SECTION TRIPLOBLASTICA, OR BILATERIA

SUBSECTION ECDYSOZOA

PHYLUM ARTHROPODA

SUBPHYLUM CHELICERATA

SUPERCLASS ARACHNIDA

CLASS OPILIONES

Like pseudoscorpions, harvestmen are a widely distributed group of arachnids found from the tropics to the polar Regions of the Earth. They inhabit A wide variety of biotopes—from damp forests to dry steppes and deserts—with some species living high in the mountains near the snowline. Harvestmen are also common inhabitants of large cities.

Over 3,600 species are known, but their actual diversity in nature is undoubtedly much greater. Harvestmen remain poorly studied in Ukraine, where 42 species have been recorded, among which the most common are Opilio parietinus and Phalangium opilio (Fig. 300). Their coloration is typically grayish, brown, or black, though brightly colored species also occur.

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Fig. 300. Harvestman Phalangium opilio (from Lange)

Morphology. The small body of a harvestman (1–10 mm, rarely up to 2 cm) consists of a prosoma (cephalothorax) and a segmented opisthosoma (abdomen); in many species, the abdominal tergites fuse with the prosomal shield into a single dorsal carapace.

The chelicerae are chelate and short, except in species that feed on terrestrial Mollusks, where the chelicerae can be longer than the body. The pedipalps are either small and leg-like or more massive, terminating in a claw and bearing spines on their segments. The basal segments of the pedipalps and anterior legs feature gnathobases (jaw lobes). The leg segments are usually very long, with secondarily subdivided tarsi that may contain up to 100 segments. These legs easily wrap around grass stems and securely hold the animal. The legs readily autotomize and, once detached, continue to undergo convulsive twitching for some time, appearing to "scythe" or "mow"—which is one of the theories explaining their common Ukrainian name ("kosaryky", meaning mowers). Another interpretation is that harvestmen appear in the greatest numbers during the hay-making season.

Like most arachnids, harvestmen are predators, feeding primarily on small insects, while some species prey on small mollusks; however, quite a few species consume decaying animal and plant matter. They ingest not only liquid food but solid particles as well.

Harvestmen breathe using well-developed tracheae, much like solifuges.

Reproduction. Females possess an ovipositor, while males have a tubular copulatory organ, and true copulation is characteristic of this group. Using the ovipositor, females lay fertilized eggs in the soil, damp moss, leaf litter, etc. The eggs are coated with adhesive secretions. Some harvestmen develop with elements of metamorphosis: their juveniles differ significantly from the adults.