The Main Line of the Evolution of Articulata—From Polychaetes to Insects

Abstract

The key points of the main evolutionary line of Articulata, leading from polychaetes to insects, are considered. The far-reaching similarity of the most primitive insects, jumping bristletails, with malacostracans, especially syncarids, leaves no doubt about the origin of the former directly from the latter. The similarity of mayfly nymphs to bristletails indicates that the evolution of Pterygota began with amphibiotic Palaeoptera. Myriapods are secondarily simplified descendants of early hexapods, having lost the division of the body into the thorax and abdomen and other ancestral characters due to transition to a cryptic lifestyle. Entognathous hexapods illustrate the initial stages of myriapodization of bristletails. Following Sharov, insect ancestry can be traced back into deep time via crustaceans to trilobitomorphs, Megacheira, and further to the most ancient arthropods, dinocarids—with grasping antennae but without walking legs! Many structural features of arthropods were formed in Polychaeta—the most primitive Articulata. The group most similar to arthropods are scale worms (Aphroditacea). By analogy with myriapods and entognaths, lobopods and non-arthropodan Ecdysozoa should be interpreted as side branches, which emerged from the dinocarid root of Arthropoda and simplified their body plans. Transformations of body plans occurred through heterochronies and heterotopies (including gamoheterotopies).