Cryptic speciation among morphologically homogeneous species is a phenomenon increasingly reported in cosmopolitan marine invertebrates. This situation usually leads to the discovery of new species, each of which occupies a smaller fraction of the original distributional range. The resolution of the taxonomic status of species complexes is essential because species are used as the unit of action for conservation and natural resource management politics. Before the present study, Ommastrephes bartramii was considered a monotypic cosmopolitan species with a discontinuous distribution. Here, individuals from nearly its entire distributional range were evaluated with mitochondrial DNA (cytochrome c oxidase subunit I and 16S rRNA). Four distinct species were consistently identified using four molecular species delimitation methods. These results, in combination with morphological and metabolic information from the literature, were used to resurrect three formerly synonymized names (Ommastrephes brevimanus, Ommastrephes caroli and Ommastrephes cylindraceus) and to propose revised distributional ranges for each species. In addition, diagnostic characters from the molecular sequences were incorporated in the species description. At present, only one of the four newly recognized species (Ommastrephes bartramii) is commercially exploited by fisheries in the North Pacific, but it now appears that the distributional range of this species is far smaller than previously believed, which is an essential consideration for effective fisheries management.

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Aristeus alcocki Ramadan, 1938 is a deep sea penaeid shrimp that forms a major commercial fishery in the Indian coast. However, the spawning population of this species along the Indian coast is poorly known. To study this, stock structure of A. alcocki using truss morphometry was employed. A total of 1842 matured specimens were collected from five geographical locations (Tuticorin (SET), Chennai (SEC), Nagapattianam (SEN), Sakthikulangara (SWS), and Kalamuku (SWK)) along the Indian coast. Thirty-nine truss distances were extracted from each specimen and analyzed by multivariate methods via principal component analysis (PCA), discriminant functions (DF) and hierarchical cluster analysis. The results of PCA analysis indicate that the first two components cumulatively explained >70% (female: 72.1%; male: 71.5%) of the total morphometric variation. Stepwise discriminant function analysis indicated abdominal variables significantly discriminated the populations at different locations. The results clustered the five samples into a minimum of two groups, group-I included the samples from SWK while rest of the samples clustered in group-II. Morphometric variation between the groups was significant for each sex. Significant differences between the groups may be attributed to geographical and environmental conditions suggesting separate management strategies for the resource sustainability.