Life History And Biology

Opiliones are oviparous and deposit between one (in cyphophthalmids) and several hundred (in phalangiids) eggs. Life cycles and longevity are variable. Many species live 1 year, with embryonic development occurring during the winter, with hatching in the spring, and reaching maturity in the fall, after five to seven molting periods. This is the typical seasonal life history of most Northern Hemisphere phalangiids. Others have an overlap of adults and juveniles throughout their life cycles during the favorable seasons, dying in the winter. Finally, cyphophthalmids and most laniatorids live several years, with cases recorded up to 5 years.

Sexual dimorphism is evident in some species. All cyphophthalmid males have a spur on the tarsus of the fourth walking leg. This structure, named an adenostyle, possibly secretes a pheromone. The families Pettalidae and Sironidae in the Cyphophthalmi have male anal glands, and the pettalids may have extreme modifications of the male anal regions.

Opiliones are generally small to medium in size (body measuring less than 1 mm to almost 2.5 cm in the European species Trogulus torosus), inhabit all types of moist to wet habitats, and occur on all the continents. The Laniatores include the large (up to more than 2 cm) and the most colorful Opiliones, and their distribution reaches a peak of diversity in tropical regions and in the Southern Hemisphere. The Eupnoi and Dyspnoi are more widely distributed, but especially abundant in the Northern Hemisphere. Finally, the Cyphophthalmi are distributed more uniformly worldwide, but are the smallest (down to 1 mm) and most obscure of the Opiliones.

No Opiliones are harmful to humans, and they do not contain any type of venom or other substance. Some Opiliones are reported as highly poisonous although not having the capacity of biting humans. This myth seems to be a confusion with the highly neurotoxic venom of some spiders. These are differentiated from Opiliones by the presence of a waist that separates the prosoma from the opisthosoma, among many other characters. In fact, Opiliones are supposed to be beneficial, and they are good indicators of undisturbed environments.

See Also the Following Articles

Arthropoda and Related Groups • Spiders

Further Reading

Edgar, A. L. (1990). Opiliones (Phalangida). In "Soil Biology Guide" (D. L.

Dindal, ed.), pp. 529-581. Wiley, New York. Giribet, G., Edgecombe, G. D., Wheeler, W. C., and Babbitt, C. (2002). Phylogeny and systematic position of Opiliones: A combined analysis of chelicerate relationships using morphological and molecular data. Cladistics 18, 5-70. Hillyard, P. D., and Sankey, J. H. P. (1989). "Harvestmen." Brill, Leiden. Shear, W. A. (1982). Opiliones. In "Synopsis and Classification of Living Organisms" (S. P. Parker, ed.), pp. 104-110. McGraw-Hill, New York.

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