Articulata and Ecdysozoa

Abstract

Science has accumulated to date such amounts of valuable and diverse information that no scientists can be encyclopedists (like those of the 17th and 18th centuries). Now every scientist is usually well informed only in one particular area and often needs consultations of other specialists. The current situation in biology is similar. In addition to evolutionary morphology, which represents fundamentals of zoology, there is a new, clearly cutting-edge and progressive area of studies, molecular genetics, which has already revealed many important general biological patterns. But the conclusions that follow from examining natural phenomena from this new point of view using new methods sometimes prove to be at odds with conventional notions. Considerable controversies have emerged on the phylogenetic position of the type Arthropoda. The peculiar features of the general body plan and the type of development of these animals seem to give evidence that they evolved from Annelida, with which they are often combined under the name Articulata. But attempts have been made to replace this concept by the idea that the clade Ecdysozoa, which includes Arthropods as well as such animals with low levels of organization as Nematoda and Priapulida, emerged early in the evolution of Bilateria. The main reason for combining the said animals in this clade is the fact that they have molts regulated with ecdysone; this point of view is supported by molecular genetic arguments. Although in this review this controversial problem is considered from the morphological point of view, the main purpose of the review is to emphasize the need to establish mutual understanding between morphologists and molecular biologists and carefully find out the causes of the existing disagreements. Rather than ideological opponents, the two areas of science should be allies helping each other to solve complicated problems.