Paleoptera

Abstract

In the infraclass Paleoptera are the orders Ephemeroptera (mayflies) and Odonata (drag- onflies and damselflies), the living species of which represent the few remains of two formerly very extensive groups. Although both are placed in the Paleoptera, authorities disagree on whether thetwoorders are monophyleticor have separate origins (see Chap- ter 2, Section 3.2). Even if monophyletic, theEphemeroptera and Odonata are two very different groups that must have diverged atavery early stage intheevolution of winged insects. They possess the following common features that unite them as Paleoptera: wings that cannot be folded back against the body when not in use, retention of the anterior median wing vein, netlike arrangement of wing veins (many crossveins), aquatic juve- nile stage, and considerablechange from juveniletoadult form. In members ofboth orders, wingdevelopment is external,though this feature is not, of course, restricted to Paleoptera.