Overview

Brief Summary

Arachnids are a class (Arachnida) of joint-legged invertebrate animals in the subphylum Chelicerata. All arachnids have eight legs, although the front pair of legs in some species has converted to a sensory function, while in other species, different appendages can grow large enough to take on the appearance of extra pairs of legs. The term is derived from the Greek word ἀράχνη (aráchnē), meaning "spider" (Oxford English Dictionary).

Almost all extant arachnids are terrestrial. However, some inhabit freshwater environments and, with the exception of the pelagic zone, marine environments as well. They comprise over 100,000 named species, including spiders, scorpions, harvestmen, ticks, mites and Solifugae (Cracraft & Donoghue, 2004).

  • "Arachnid". Oxford English Dictionary (2nd ed.). 1989.
  • Joel Cracraft & Michael Donoghue, ed. (2004). Assembling the Tree of Life. Oxford University Press. p. 297.
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Physical Description

Morphology

Sexual Dimorphism

Females generally larger than males and this can be pronounced; Sexual Dimorphism often also in shape and color; male spiders have specialized intromittent appendages (pedipalps).
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Ecology

Associations

Known predators

Arachnida (arachnids (unspec.)) is prey of:
Geothlypis trichas
Myiarchus
Baeolophus bicolor
Sitta carolinensis
Vireo olivaceus

Based on studies in:
USA: Illinois (Forest)

This list may not be complete but is based on published studies.
  • A. C. Twomey, The bird population of an elm-maple forest with special reference to aspection, territorialism, and coactions, Ecol. Monogr. 15(2):175-205, from p. 202 (1945).
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Known prey organisms

Arachnida (arachnids (unspec.)) preys on:
Diptera
Phaenicia eximia
Hemilucilia segmentaria
Cochliomyia macellaria
Paracoenia turbida
Lamproscatella dichaeta
Microcoelepis
Chironomidae
Amphipoda
Tipulidae

Based on studies in:
USA: Illinois (Forest)
Costa Rica (Carrion substrate)
USA (Temporary pool)

This list may not be complete but is based on published studies.
  • A. C. Twomey, The bird population of an elm-maple forest with special reference to aspection, territorialism, and coactions, Ecol. Monogr. 15(2):175-205, from p. 202 (1945).
  • L. F. Jiron and V. M. Cartin, 1981. Insect succession in the decomposition of a mammal in Costa Rica. J. New York Entomol. Soc. 89:158-165, from p. 163.
  • N. C. Collins, R. Mitchell and R. G. Wiegert, 1976. Functional analysis of a thermal spring ecosystem, with an evaluation of the role of consumers. Ecology 57:1221-1232, from p. 1222.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records:176522
Specimens with Sequences:123528
Specimens with Barcodes:116376
Species:8197
Species With Barcodes:6614
Public Records:109896
Public Species:3199
Public BINs:13312
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Barcode data

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