Excerpt: The arachnid genus Atypus (family Atypidae, suborder Mygalomorphae) contains four species in North America. These tarantulas are atypical because they have retained remnants of the primitive segmentation characteristic of Mesozoic spiders; the dorsum of the abdomen has tergites which differ little or not at all from those found on Oligocene spiders in the Florissant shales or in Baltic amber. The atypical tarantulas are among the most generalized of all living spiders, lacking the specialized morphological features of more advanced families. They lack reduction, migration, or enlargement of eyes; they have simple dry silk glands only; their legs lack specialization for running or silk handling; the carapace is unspecialized.
This genus seems to remain successful in interspecific competition, not because of morphological specialization, but due to behavioral uniqueness. The spider constructs a vertical tube web from an underground burrow up the trunk of a tree. The web acts as a shield, making the spider unrecognizable as a potential predator. The prey is attacked through the silk, pulled inside the tube, and sucked dry. Afterwards the carcass is thrown out and the tube is repaired.
Bixler, David E.
"The Tarantula Atypus Milberti in Michigan (Araneae: Atypidae),"
The Great Lakes Entomologist: Vol. 2
, Article 7.
Available at: http://scholar.valpo.edu/tgle/vol2/iss1/7