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Family Thomisidae - Crab Spiders

Spider ID - Tmarus Crab spider-Misumenoides formosipes  - Misumenoides formosipes ?Xysticus - Xysticus punctatus M. dubia - ventral - Mecaphesa dubia - female spider - Xysticus Crab Spider - Bassaniana versicolor Crab Spider - Mecaphesa - female Xysticus funestus - male
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Chelicerata (Chelicerates)
Class Arachnida (Arachnids)
Order Araneae (Spiders)
Infraorder Araneomorphae (True Spiders)
No Taxon (Entelegynes )
Family Thomisidae (Crab Spiders)
Synonyms and other taxonomic changes
Note that many of the crab spiders in the genus Misumenops were transferred to the genus Mecaphesa in 2008 (see Lehtinen, P. T. & Y. M. Marusik. A redefinition of Misumenops F. O. Pickard-Cambridge, 1900 (Araneae, Thomisidae) and review of the New World species. Bull. Br. arachnol. Soc. 14: 173-198). This change is now reflected in our BG taxonomy.
Numbers
130 species in 9 genera in our region, although some authors split them into 10 genera (1).

We have 14 genera following the world spider catalog.
Identification
See discussion on identification of three common flower-inhabiting genera (Misumena, Misumenoides, and Misumenops (Mecaphesa)) here.
Remarks
Spiders with very small (if strong) jaws (such as crab spiders and cobweb weavers) make small holes in the prey and vomit their digestive fluid into the prey's body, the end result being a hollow shell with some or most of the muscles and internal organs digested and sucked out. (2)

You can see an example of this feeding behavior in the following image:
Internet References
University of Kentucky Entomology Dept. - Information specifically about Crab Spiders
A Good Web Page About Crab Spiders - Lots of pictures and information about Crab Spiders, even those found in Europe
AMNH page with key to genera: Thomisidae .
~ PDF - Schick, R. X., 1965. The crab spiders of California (Araneae, Thomisidae). Range maps, keys, descriptions, & drawings of palps/epigynes.
Works Cited
1.Spiders of North America: An Identification Manual
D. Ubick, P. Paquin, P.E. Cushing and V. Roth (eds). 2005. American Arachnological Society.
2.The Spider Myths Site