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SEM image of the week: Eight is enough

Posted on Monday, May 7, 2012 by for SEM.

The subject of this week’s scanning electron microscope image is a spider that crawled out from behind a painting in my parents’ apartment. Everyone knows that spiders have eight legs, but fewer people know that spiders have six to eight eyes. We originally thought this specimen was a wolf spider, but they have two large eyes on the top row and four smaller eyes on the bottom row. Our guest in the Midwood Science SEM has two sets of four equally sized eyes and is possibly a nursery web spider. There are currently over 450 defined species of spiders, but there may be four times as many species yet to be discovered.

Your basic spider has two main body parts — a cephalothorax at the front and an abdomen at the rear. In addition to the eight legs, spiders also have two long appendages for grasping food (called pedipalps) and two short appendages for injecting venom (called chelicerae). Spiders extrude silk for their webs from glands connected to a hollow set of appendages (called spinnerets) at the far back end of the abdomen.

Overhead view of the cephalothorax Close up of four of the eyes A slightly different overhead view showing the eyes, pedipalps (extended forward), and chelicerae (folded under the animal)
Underside view of the cephalothorax with a good view of the mouthparts (chelicerae closer to the mouth, pedipalps closer to the legs) Underside view of the abdomen showing the spinnerets Close up of the spinnerets
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