TO ORIGIN OF CLADOCERA (CRUSTACEA, BRANCHIOPODA): NEW UNDERSTANDING OF THE OLD HYPOTHESIS

摘要

The comparative analysis of representatives of two sister taxa, Cladocera and Cyclestherida, showed that the pedomorphic morphology of cladocerans (the small number of thoracic segments and segments of antennae II, reduction of carapace) was caused by the stop of development of the somatic structures at early larval stages. This stop is not related to the accelerated development of the sexual system (progenesis) of Cladocera, since it takes place long before the beginning of their reproduction. In this connection, the past hypotheses that cladocerans have evolved from the reproducing larvae of the ancestral form or they are the early matured metanauplii should be recognized erroneous. The origin of Cladocera from the Cyclestheria-like ancestor is regarded neotenic taking into consideration the broadened interpretation of this term.