Jumping spider - Phidippus mystaceus

	Moustache Jumping spider - Phidippus mystaceus Family Salticidae - Jumping Spiders Live adult spiders photographed at Fort Bragg, North Carolina. Spider Index \| Spider Main \| Funnel Web \| Orb Web \| Nursery Web \| Cobweb \| Insects

The 'moustache' jumping spider has my vote as one of the most colorful. (The species epithet mystaceus is derived from the Greek mystax, a cluster or row of hairs above an insect's mouth, roughly analogous to a human moustache.) It is a spider that offers a photographer a good chance of capturing images of the spider's retina, which is not fixed in place like our own. The jumping spider's retina is moveable. Because the retina is the darkest part of the eye, you can sometimes look into the eye of a jumping spider and see it changing color as it moves to follow your actions. When it is darkest, you know the spider is looking straight at you, because then you are looking straight into its retina.

Jumping spiders have excellent vision, among the highest acuity in any invertebrate. The eight eyes are grouped four on the face 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 sits on top of the eyes and brain. [1]

Jumping spider's anatomical points of interest:

Esophagus passes 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

Here is an interesting video of this species

References

Bugguide.net, Phidippus mystaceus
Jumping Spider Vision David Edwin Hill, licensed under the Creative Commons Attribution 3.0 Unported

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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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