**Donggu Jeon 1, Wonchoel Lee 2, Ho Young Soh <sup>3</sup> and Seong-il Eyun 1,\***


http://zoobank.org/urn:lsid:zoobank.org:pub:36893F6D-A5D0-46C1-9D56-9FABBD6BF212 Received: 27 November 2019; Accepted: 18 December 2019; Published: 20 December 2019

**Abstract:** Male monstrilloid copepods, described herein as *Monstrillopsis paradoxa* sp. nov., were collected from the Chuja Islands, Jeju, Korea, using a light trap. They display many of the common features of *Monstrillopsis*, including large, prominent eyes, an anteriorly positioned oral papilla, and four setae on each caudal ramus. Type-2 modification of the antennules further supports the assignment of the new species to *Monstrillopsis*. However, the present specimens have an unusually low number of urosomal somites, just three in total, compared to five in males of all congeneric species, and from four (in *Cymbasoma*) to five in males of all other monstrilloid genera. Up until now, in the Monstrilloida only females of *Cymbasoma* have been known to have as few as three urosomal somites.

**Keywords:** Monstrillidae; *Monstrillopsis paradoxa* sp. nov.; *Monstrillopsis planifrons*; morphological taxonomy; tagmosis; male genitalia; pore pattern; male/female matching; marine invertebrate host; semi-parasitic; Korea
