BIO 385 Invertebrate Zoology
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Invertebrate Diversity
Phylum Arthropoda
Class Arachnida

Return to Main Arthropod Page

Arachnid Characteristics

  • Additional feeding appendages: pedipalps & maxilla
  • 4 pairs of walking legs
  • Lack abdominal appendages (except for spinnerets in some)
  • Nearly all are terrestrial
  • Respiration via book lungs or trachea

Class Arachnida

Order Acari

  • Ticks and mites
  • Most very tiny (< 1 mm)
  • Very diverse
  • Some are external parasites
Hard Tick
Hard Tick, Dermacentor sp.; CA
Predatory Mite
Predatory Mite, AZ
Unid Mite
Blue Oat Mite, Penthaleus sp.; AZ

Order Araneae

  • Spiders
  • 36,000 Species
  • Most are predators
  • Chelicerae modified into venom fangs
  • Silk glands and spinnerets
Nursery Web Spider
Nursery Web Spider (Pisauridae); Ecuador
Banded Agriope
Banded Agriope, Argiope trifasciata; Kenya
Crab Spider
Goldenrod Crab Spider, Misumena vatia; ME
Long-jawed Orb Weaver
Long-jawed Orb Weaver. Tetragnatha sp. (Tetragnathidae); AZ
Jumping Spider
Jumping Spider Phidippus sp. (Salticidae); AZ
Wolf Spider
Wolf Spider, Hogna sp. (Lycosidae); KY

Order Opiliones

  • Harvestmen & Daddy-Long-Legs
  • Small bodies but very long legs
  • Predators or scavengers
  • 1 Pair of eyes
  • Reduced chelicerae
Daddy Long Legs
Brown Daddy-long-legs, Phalangium opilio; KY
Brown Daddy Long Legs
Brown Daddy-long-legs, Phalangium opilio; KY
Ornate Harvestman, Vonones ornata; KY

Order Scorpiones

  • Scorpions
  • Abdomen divided into Mesosoma and "tail"
  • Large pedipalps form pincers (chelae)
  • Venomous stinger at end of tail
  • Reduced chelicerae
Sand Scorpion
Coachella Valley Sand Scorpion, Paruroctonus mesaensis; carrying young.
Uroctonus Scorpion
California Forest Scorpion, Uroctonus mordax; CA
Northern Scorpion
Northern? Scorpion, Paruroctonus boreus?; UT

Order Pseudoscorpiones

  • Pseudoscorpions
  • Large pedipalps form pincers (chelae)
  • Abdomen lacks elongated "tail" and stinger
  • Size tiny; often phoretic on beetles
Pseudoscorpion whole mount
Pseudoscorpion, whole mount microscope slide
Pseudoscorpion; AZ
Pseudoscorpion; AZ

Order Solifugae or Solpugida

  • Sunspiders or Windscorpions
  • Very large forward-pointing chelicerae
  • Appear to have 5 pairs of legs: the anterior pair is actually enlarged leg-like pedipalps used as feelers
  • Fast-running predators
Wind Scorpion
Straight-faced Wind Scorpion, Eremobates sp.?, male; AZ
Wind Scorpion female
Straight-faced Wind Scorpion, Eremobates sp.?, female; AZ
Sun Spider
Sun Spider; dried specimen

Order Uropygi

  • Whipscorpions or Vinegaroons
  • Enlarged pedipalps but with reduced chelae
  • Flattened body
  • First pair of walking legs longer and slenderer than others, act as feelers
  • Posterior end with a thin, straight telson that squirts acetic acid
Philippine Vinegaroon, Minbosius manilanus
Giant Vinegaroon, Mastigoproctus giganteus

Order Amblypygi

  • Tailless Whipscorpions
  • Pedipalps with spikes but not jointed chelae
  • Flattened body
  • First pair of walking legs extremely long (at least several times length of other legs) and function as feelers
  • Lack telson
Sonoran whipscorpion
Sonoran Whipscorpion, Paraphrynus mexicanus (native to southern Arizona)
Florida Whipscorpion, Phrynus marginemaculatus; FL
Whip Spider
African Whipspider, Damon variegatus
This page last updated 28 June 2015 by Udo M. Savalli ()
Images and text Udo M. Savalli. All rights reserved.