HYPERIIDEA

Hyperiid amphipods are exclusively marine, pelagic crustaceans with a vide vertical distribution in the oceans. Approximately 260 species have been described worldwide.
Typical hyperiid has plump, rounded body and large eyes occupying most of lateral surface of deep, globular head. The suborder is also characterized by lack of maxilliped palp, fusion of second and third urosomal segments and the absence/ small size of the coxa. Some hyperiids are luminescent.
Many hyperiids show complex life-cycles involving symbiotic relationships with gelatinous zooplankton such as scyphozoan medusae, siphonophores, ctenophores or salps, but some are free-living predators. For example, Themisto abyssorum and Themisto libellula , essential components of Arctic pelagic ecosystems, prey on copepods, euphausiids, pteropods and chaetognaths.