A team of biologists from the IEE RAS and the Faculty of Biology of Moscow State University studied the common tropical nudibranch mollusc Coryphellina rubrolineata. Molecular genetic analyzes, as well as a study of the external and internal structure of animals, showed that this is not one species, but at least five. As a result, the authors described four new species of nudibranch mollusks that differ in mitochondrial and nuclear genes, as well as body stripes. The study was supported by a grant from the Russian Science Foundation (RSF), the results were published in the journal Diversity. Molecular genetic methods have allowed scientists to better identify cryptic (similar in appearance, but genetically different) and pseudocryptic (different in appearance, but this becomes clear only after applying genetic methods) species and species complexes. With their spread in taxonomy, the hypothesis of the leading role of geographical barriers and spatial isolation in speciation began to dominate. Often, remote populations of the same species with a wide range began to be divided into several species, based solely on genetic comparison data, which is not always justified. Recent studies in the field of evolution and phylogeny emphasize the great role of the ecological factor in speciation: organisms can diverge into different ecological niches within the same geographical area, acquiring new characters and isolating according to their "way of life."