Morphogenesis of small springtails species from the genus Megalothorax (Collembola: Neelidae).

In this work, we describe for the first time the complete sequence of chaetotaxy development for Megalothorax bokovae and the second stage chaetotaxy for Megalothoraxperspicillum. The chaetotaxy development of the body is similar in these two species: at the juvenile stages, the chaetotaxy of the first segment of the thorax and the last segments of the abdomen is more developed, while the chaetotaxy of the two last segments of the thorax and the first segments of the abdomen is not developed. In addition to the increase in the number of chaetae, during the process of Megalothorax morphogenesis, the size and shape of the sensillar apparatus changes. All this suggests that the genus Megalothorax is characterized by such evolutionary strategies as neochaetosis and heterochaetosis. This study will promote the future use of chaetotaxic traits in the taxonomic and phylogenetic studies of Megalothorax, and will potentially illuminate the early evolution of Neelipleona.