Researchers from the American Museum of Natural History, the National Museum of Namibia, and Texas A&M University have created a visual atlas and dictionary of terms for the many strange features that adorn the fearsome-looking jaws of a little known group of arachnids. Called camel spiders, baardskeerders [beard-cutters], sun spiders, wind scorpions, and other colorful names, Solifugae are an order of arachnids that are neither spiders nor scorpions, and are notable for their intimidating jaws.
This arachnid, Galeodes sp., is one of about 1,100 species in the order Solifugae. © Igor Siwanowicz
In research out today in the Bulletin of the American Museum of Natural History, the scientists present the first comprehensive analysis of jaw morphology across Solifugae. Their jaws, or chelicerae, are the largest for body size among the group of animals that possess these specialized mouthparts—including horseshoe crabs, sea spiders, and arachnids—and bear most of the structures used for their classification. Despite their prominence in folklore around the world, these animals, known as solifuges, have scarcely been studied, and much remains unknown about their biology.
“Our limited understanding of the incredible jaws of these arachnids, together with terminology that is unstandardized and even contradictory, has hindered our ability to classify them and figure out where they fit in the arachnid tree of life because, much like the cranial anatomy of vertebrates, the jaws of solifuges contain most of the relevant information,” said Lorenzo Prendini, a curator in the Museum’s Division of Invertebrate Zoology and an author on the paper.
The jaws of camel spiders in the subfamily Dinorhaxinae and the family Rhagodidae. © Tharina Bird
There are about 1,100 species of camel spiders, which range in size from a few millimeters long to about 15 centimeters (6 inches) in length. The arachnids look like big, hairy spiders with an extra pair of legs—which are really pedipalps, leg-like structures ending in an adhesive sucker, and used like arms for grasping, holding, and climbing. While they have numerous characteristics that distinguish them from other arachnids, the jaws of camel spiders are often their most distinctive trait.
Examples of the variety of arachnids in the order Solifugae
© Alexander Gromov (A, B), Simon van Noort (C), Sanjay Das (D)
“In most solifuge families, species identification is based primarily on features of the jaws, yet no comprehensive survey of these character systems has ever been done,” said Tharina Bird, a senior curator at the National Museum of Namibia and lead author of the paper.
Combining observations from high-resolution microscopy of the specimens’ jaws with existing literature, the researchers proposed nearly 80 terms—many of them new—for structures of similar appearance and position, to serve as common language for future work. By creating a defined vocabulary for these structures, the authors hope to help other researchers more accurately and easily identify and understand all species of camel spiders.