The Phyloperiodic Approach Removes the “Cryptic Species” and Puts forward Multilevel Organismal Diversity

The notion of the “cryptic species” has recently become an important agenda in biodiversity research. In this study, we show, by applying a periodic-like morphological and molecular framework to the nudibranch genus Cadlina from the world’s least explored locations in the Kuril Islands in the northwestern Pacific, including a description of six new species, that the term “cryptic species” should be removed from biodiversity research terminology. We explicitly show that different species of this complex have various degrees of molecular phylogenetic distances and morphological distinctness, revealing a truly multilevel system of fine-scale differences and similarities. Therefore, to designate any of these species as “cryptic” or “non-cryptic” would be completely arbitrary, non-operational, and generally meaningless. By this, we finally strongly propose to remove the notion of “crypticity” and the term “cryptic species” (in the sense of an “indistinguishable species”) from the arsenal of modern biology, including phylogeny and taxonomy. The importance of fine-scale species differentiation in the multilevel framework is shown for addressing conservation and global warming challenges. Six new species are named after scientists who have not always received the honours they deserve, including two women who did not receive their respective Nobel Prizes.