Naturalist Newsletter of March 31, 2008
written in the community of 28 de Junio, in the Central Valley,
8 kms east of Pujiltic, Chiapas, MÉXICO
about 800 meters in elevation, ± LAT. 16° 18'N, LONG. -92° 28'W.
One of the hardest parts of preparing for a long trip living out of a backpack is deciding which books to take. When I began my current wandering in October, 2006, one book I brought with me was the little Golden Nature Guide A Guide to Spiders and Their Kin, published in 1968. It qualified because it was small, and down here you're always meetinging arthropods you can't classify. This week I was glad to have the little book when among some rocks I found what's shown below:
That's not the animal itself, but rather the creature's abandoned exoskeleton, or "skin," the main body being about an inch long. Arthropods are encased in stiff exoskeletons so, as they grow, periodically their old exoskeletons split, the animals emerge from them, and then hide in safe places until their new, larger, but temporarily soft exoskeletons harden. If you look closely at the picture you can see how the body's broad, roundish central part (its carapace) has split along its sides and front, then hinged upward like the lid of a tin can, with the hinge at the back. The animal crawled out of its old exoskeleton through this opening.
The creature's spiny, front "arms" look a lot like a scorpion's, but scorpions bear long, slender, segmented tails with stingers at their ends. This animal has no tail. It's some other kind of "spider kin," as the Golden Guide phrases it.
Near the scorpion order in my little book lie the pseudoscorpion, windscorpion, whipscorpion and tailess whipscorpion orders. I mention the order groupings to make it easier to visualize how closely related the groupings are. Among birds, for instance, we speak of the woodpecker order, the penguin order and the passerine or songbird order. Among arthropod orders there's a similar relationship.
It turns out that the mystery exoskeleton is that of a tailless whipscorpion, described by my little Guide as native to tropical America, Africa and Asia, and hot, humid parts of the US South. Tailless whipscorpions hide under bark or stones and when disturbed scurry sideways like a crab.
Members of the tailless whipscorpion order are distinguished by their first pair of legs being long and whiplike. Unfortunately, the whiplike legs were too fragile to survive my transport, though a slender fragment of one leg is stuck to other legs at the right in the picture.