Hyperoche shihi sp. nov. (Crustacea : Peracarida : Amphipoda): a symbiont of a deep-living medusa in the Gulf of California

From samples of deep-water zooplankton obtained in the Gulf of California, an undescribed species of the genus Hyperoche Bovallius was collected. The new species is similar to Hyperoche medusarum Kroyer and Hyperoche luetkenides Walker. It differs from its congeners mainly by the strong, large chela of pereopod 2 and the absence of processes or denticles along the posterior distal margin of same structure. It was collected at a depth of 1136 m as a symbiont of the bathypelagic hydromedusa Chromatonema erythrogonon (Bigelow). The amphipod remained grasped to the medusa subumbrellar cavity. Seven other associations are known between hyperiids and jellies in the Gulf of California, most from the epipelagic layer. This is the only deep-living species of Hyperoche known.