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Genus Xysticus - Ground Crab Spiders

Spider - Xysticus Xysticus ellipticus - male spider - Xysticus luctans - male large crab spider? - Xysticus Xysticus Wide Armspan - Xysticus - male Crab Spider - Xysticus - female Unidentified spider - Xysticus
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Chelicerata (Chelicerates)
Class Arachnida (Arachnids)
Order Araneae (Spiders)
Infraorder Araneomorphae (True Spiders)
No Taxon (Entelegynae)
Family Thomisidae (Crab Spiders)
Genus Xysticus (Ground Crab Spiders)
Pronunciation
ZIS-ti-kuhs(1)
Synonyms and other taxonomic changes
Explanation of Names
A Latin loan word from Greek.
Refers to the manner in which atheletes would clean themselves before the invention of the shower.(1)
Numbers
67 species in NA.(1)
Size
Females 5-10mm; males around 4mm.
Identification
Xysticus usually has a well defined dorsal stripe on the carapace:

The anterior and posterior lateral eyes are on incompletely conjoined tubercles(1):

Tibia 1 with more than two pairs of ventral macrosetae and femur 1 slender (about four times longer than wide)(1):


* Ozyptila and Xysticus are both distinguished from either Coriarachne or Bassaniana by the lateral profile of the carapace: as Lynette mentioned, in both Coriarachne and Bassaniana the carapace is roughly flat all the way from front to back. The side profile of the carapace for Ozyptila and Xysticus, on the other hand, will be higher near the front and will drop down near the back at around coxa three. Coriarachne and Bassaniana maintain roughly the same level height from front to back.

So, the order of things to check when separating Xysticus, Ozyptila, Coriarachne and Bassaniana is:

1) Check carapace flatness first, to separate Coriarachne and Bassaniana from Ozyptila or Xysticus

2) Then, check the ventral macrosetae on tibia I and femur I length/width ratio to separate Xysticus from Ozyptila.

Ozyptila: - no more than 2 pairs of ventral macrosetae on tibia I .... femur I length-to-width ratio is about 3:1

Xysticus: - 3 to 4 pairs of ventral macrosetae on tibia I .... femur I length-to-width ratio is about 4:1

Anyway, that's how I've been separating these genera, using the information from Spiders of North America, Ubick et al. (2005) page 247. ~ John Sloan 2 Aug. 2009
Range
Widespread in NA.(1)
Habitat
Generally found on ground or close to it.
Food
Insects, spiders.
Remarks
Very similar appearance to Coriarachne, Bassaniana, and Ozyptila.
Internet References

~ crawford.tardigrade.net - Xysticus benefactor female & male from WA.
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.