Taxonomic revision of the genus Nannomesochra Gurney, 1932 (Copepoda, Harpacticoida) with description of three new species

A taxonomic revision of the genus Nannomesochra Gurney, 1932 was made based on the material collected from a wide range of localities along the Turkish coasts. Detailed morphological examination and comparisons of several specimens as well as the previous descriptions which were assigned to the so-called cosmopolitan species N. arupinensis (Brian, 1925) revealed that N. arupinensis indeed represents a complex of several closely related morphospecies that can be differentiated from one another by only detailed observations. With this study, Nannomesochra parvula (Gurney, 1927) was reinstated and redescribed because of the setation of the swimming legs and the structure of the P5 in female. It has been determined that, according to updated modern keys, the recent inclusion of the monotypic genus Archeolourinia Corgosinho & Schizas, 2013 in the Louriniidae Monard, 1927 is not justified since Archeolourinia shermani Corgosinho & Schizas, 2013 does not belong to this family but must be assigned to the genus Nannomesochra within Canthocamptidae. Therefore, Archeolourinia was removed from the family Louriniidae and accepted as junior synonym of Nannomesochra keeping Nannomesochra shermani (Corgosinho & Schizas, 2013) comb. nov. as a valid species of the genus. As a result of the morphological examination of Turkish material, 3 new species of Nannomesochra were discovered and named as N. gebekumensis sp. nov., N. giziri sp. nov., and N. erythraiensis sp. nov. With addition of these species mentioned above, the genus now contains seven valid species, namely, N. arupinensis, N. parvula, N. zavodniki Petkovski & Apostolov, 1974, N. shermani comb. nov., N. gebekumensis sp. nov., N. giziri sp. nov., and N. erythraiensis sp. nov. Detailed review of the previous species records is given, indicating that the genus Nannomesochra has a worldwide distribution. But it is concluded that almost all of the previous records are unreliable, since they do not contain sufficient information to verify to which Nannomesochra species they belong. The phylogenetic position of Nannomesochra within Hemimesochrinae Por, 1986 was also evaluated in the study and a generic key within the subfamily is presented. It was concluded that the presence of the three elements on the distal endopodal segment of the P3 endopod in the male can be defined as an autoapomorphy of the genus Nannomesochra.