Jumping Spider - Phidippus princeps
Family Salticidae - Jumping Spiders
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Live adult jumping spiders  photographed at northern Illinois

Jumping Spider - Phidippus princeps

Jumping spiders have excellent vision, among the highest acuity in invertebrates. The eight eyes are grouped four on the face (the two big anterior median eyes in the middle, and two smaller anterior lateral eyes to the side), and four on top of the carapace. The two large, forward-facing eyes (AME) are tubular behind the lens, with a well-developed musculature, unique to salticids, that supports and moves the retina - the opposite arrangement of our own eyes. [1]


Note: the function of the posterior medial eyes is unknown [2]

Spider musculature is also different from ours: in the spider, muscles operate from the inside to move external skeletal elements; our own skeletal muscles surround the elements they operate. But even these glaring differences are nothing compared to the jumping spider's brain and digestive system - their esophagus passes right through the brain, and one branch of the gut (analogous to our intestines) actually overlies the eyes and brain. [1]

Jumping Spider - Phidippus princeps
This cute little gal was holed up in her retreat web
Jumping spider's anatomical points of interest:
  • Esophagus passes straight through the brain
  • Portion of gut overlies the eyes and brain inside carapace
  • Heart extends from abdomen into cephalothorax
  • Leg muscles attached inside the carapace operate legs like marionette puppets
  • Jumping spider's brain volume to body size proportionate to human, but visual processing region is larger
  • Salticids move retinas inside the eyes to look in different directions, as the lenses are fixed in the carapace
    Jumping Spider - Phidippus princeps
    This spider's large front-facing eyes give her acute stereoscopic vision
References
  1. Bugguide.net, Phidippus princeps
  2. Jumping Spider Vision, David Edwin Hill, via Creative Commons Attribution 3.0 Unported
  3. Arthur V. Evans, National Wildlife Federation Field Guide to Insects and Spiders of North America
  4. Clark Kimberling, University of Evansville, "Thomas Say, Father of American Entomology"
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Class Arachnida / Order Araneae: Spiders are the largest group of arachnids.  They are easily recognized by their eight legs, and there are few creatures great or small that elicit such irrational fear in mankind. The vast majority of spiders are completely harmless and offer beneficial services, chief of which is keeping the burgeoning insect population in check. I am continually amazed at the resourcefulness of these supremely successful predators.
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