Redescription and Molecular Characterisation of Gnathia tridens Menzies & Barnard, 1959 (Isopoda: Gnathiidae), a Presumed Ubiquitous Nearshore Isopod from the Temperate Northern Pacific

Abstract

Purpose: Gnathia tridens Menzies & Barnard, 1959, is redescribed from material collected from San Diego, California and compared to the original description, as well as material held at the Natural History Museum of Los Angeles County and the Santa Barbara Museum of Natural History. Materials and Methods: A full redescription is given based on both morphological and molecular characteristics of the male using light and scanning electron microscopy, and COI mtDNA and ITS2 rDNA genes, respectively. Results: The key distinguishing characters that set G. tridens apart from other congeners are the equally trifid mediofrontal process, the mandible with a large incisor; the mesioventral margin anterior tip dorsally visible; pereonite 4 with distinct visible anterior constriction; and the three proximal tubercles on the antenna articles. Based on the molecular data for COI, the closest congener differs with 122 base pairs. Conclusion: Together, the combined morphological and molecular characterisation will provide a foundation for future, taxonomic, phylogenetic and biogeographical studies within the genus Gnathia and the Gnathiidae.