Nebalia Pseudotroncosoi N. Sp (malacostraca: Leptostraca), from South Korea, with a Peculiar Sexual Dimorphism

A new crustacean, Nebalia pseudotroncosoi n. sp. (Malacostraca: Leptostraca), occurs along the southern coasts of Korea. The specimens were collected by light traps in harbors where the bottom consisted of fine sand with some algal mats. The new taxon is distinguished from all other known species of Nebalia by the following characteristics: a rectangular compound eye with two to three small distal lobes; an antennular flagellum that is clearly shorter than the peduncle, with up to 10 articles; the fourth article of the antennular peduncle has only two distal thick setae; the antennular scale is nearly oval with a length that is 1.8 times the width; the second article of the mandibular palp has three distally plumose setae; pleonites 3 to 7 have rounded denticles along their posterior dorsal margins; and the protopod of pleopod 4 lacks serration along the posterior margin. We discuss sexual dimorphism in the genus Nebalia and propose the necessity of describing male traits when reporting new species. We also provide partial sequences of the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene from the new species that can be used as a molecular diagnostic characteristic.