Instant taxonomy: choosing adequate characters for species delimitation and description through congruence between molecular data and quantitative shape analysis

The lack of university funding is one of the major impediments to taxonomy, partly because traditional taxonomic training takes longer than a PhD course. Understanding ranges of phenotypic variability for different morphological structures, and their use as characters for delimitation and description of taxa, is a tedious task. We argue that the advent of molecular barcoding and quantitative shape analysis makes it unnecessary. As an example, we tackle a problematic species-complex of marine copepods from Korea and Japan, approaching it as a starting taxonomist might. Samples were collected from 14 locations and the mitochondrial COI gene was sequenced from 42 specimens. Our phylogenetic analyses reveal four distinct clades in Korea and Japan, and an additional nine belonging to a closely related complex from other parts of the Northern Pacific. Twenty different morphological structures were analysed for one Japanese and two Korean clades using landmark-based two-dimensional geometric morphometrics. Although there is no single morphological character that can distinguish with absolute certainty all three cryptic species, most show statistically significant interspecific differences in shape and size. We use five characters to describe two new species from Korea and to re-describe Tigriopus japonicus Mori, 1938 from near its type locality.This work was supported by a grant from the National Institute of Biological Resources (NIBR), funded by the ministry of Environment (MOE) of the Republic of Korea (NIBR201704101). The third author expresses special thanks to Hyunwoo Bang, Eunjung Nam, Kanghyun Lee, Jinwook Back, Dongju Lee, Kichoon Kim, Min Jae Kim, Donggu Jeon and other members of the Biodiversity Laboratory, Hanyang University, for their help in sampling and observation during this study. The scanning electron microscope was made available through the courtesy of Jin Hyun Jun (Eulji University, Seoul), and we also want to thank Junho Kim (Eulji University, Seoul) for the technical help provided. Two anonymous reviewers are acknowledged for many constructive remarks