The abundant calanoid copepod Paracalanus parvus s.l. Boeck 1865 (Calanoida, Crustacea) is a species complex with a worldwide distribution from temperate to tropical shelf waters. Due to confusion with morphologically similar species such as P. indicus or P. quasimodo as well as within the species complex itself its biogeography is not well resolved. Furthermore, P. parvus is probably often confused with other morphological similar species. The aim of the current investigation is to examine the morphological and molecular characteristics of P. parvus, P. indicus and P. quasimodo and define their geographic distribution. We analysed 100 specimens from various shelf regions of the Atlantic, Pacific and Indian Ocean, and characterized a set of morphological traits such as the distal edge of the exopod 3 of swimming legs 2 – 4 and the number of spinules on the posterior surfaces of the swimming legs for each species. A molecular delineation of the species was carried out with two mitochondrial gene fragments Cytochrome b and COI. Based on the mitochondrial barcoding data, there is molecular evidence for the existence of cryptic species within Paracalanus parvus s.l.. Among the 70 specimens in our study, we identified 4 lineages which were differentiated at a level commonly regarded as reproductively isolated species. "We will present preliminary results of the relationships within and among the specimens of P. parvus, P. indicus and P. quasimodo to provide a clearer view of the phylogeography of this ecologically important and evolutionarily successful calanoid species group.