Opisthothelae is a suborder of spiders within the order Araneae, containing Mygalomorphae and Araneomorphae, but excluding Mesothelae.

[4] Mygalomorphae have two pairs of book lungs, and have chelicerae that move vertically, allowing the spider to grasp its prey from above and below.

Araneomorphae typically have one pair of book lungs, and chelicerae which move horizontally, allowing a firmer grip.

[4] Lampshade spiders (family Hypochilidae) show some characteristics of Araneomorphae despite being mygalomorphs, and have fangs that can move diagonally.

[5] Distinguishing araneomorphs and mygalomorphs on first inspection is difficult unless the specimens are large enough to permit immediate examination of the fangs, although their differences in behavior can provide help for identification in the wild.