A new genus and species of oceanic planktonic Tisbidae (Crustacea, Copepoda, Harpacticoida) with enlarged modified eyes

Abstract

Both sexes of a new monotypic genus of Tisbidae (Copepoda, Harpacticoida) are described from the epi- or mesopelagic zone in the Kuroshio region, Japan. Gyorome guttatumgen. et sp. nov. belongs to a monophyletic lineage of deepwater holoplanktonic genera defined by a suite of characters. Within this clade, Gyoromegen. nov. appears most closely related to Neotisbella Boxshall, 1979. The most distinguishable feature of G. guttatumgen. et sp. nov. is the presence of large, paired, frontal modified eyes, each consisting of a baculiform ocellus, a globular (Gicklhorn’s?) organ, and a semi-parabolic plate. The taxonomic position of Tisbe spinulosa Bradford & Wells, 1983 is discussed and a key to the six meso- and bathypelagic tisbid species is provided. Confusion surrounding earlier literature reports of supernumerary elements on the caudal ramus in some harpacticoid taxa is clarified. Secondary modifications of ocellar components of the typical naupliar eye in the Harpacticoida are reviewed. It is suggested that the development of specialized eyes in G. guttatumgen. et sp. nov. may provide a means for detecting bioluminescent food particles in oligotrophic pelagic environments. The large, vaulted prosome indicates the species is an opportunistic macrophage that has adopted gorging as a feeding strategy.