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Abstract

A new species of deep-sea jellyfish, Crossota millsae (Cnidaria: Hydrozoa: Trachymedusae: Rhopalonematidae), is described from the North Pacific Ocean off California and Hawaii. Discrete depth sampling showed this species lives at depths below 1000 meters in both geographic locations. The species is more abundant off California than off Hawaii. The greatest population densities were found at ~2500 m off California and at ~1250 m off Hawaii. The burnt-tangerine color of the inner bell and bright pink to lavender color of the ring and radial canals, manubrium and gonads make living specimens of this species difficult to confuse with any other known species of hydromedusa. Sexually dimorphic differences in gonad morphology are evident. The pendant testes contained spermatids at various stages of spermatogenesis as observed using scanning electron microscopy. Ova develop directly into small medusae that reside subumbrellarly between the radial canals of the mother. Various developmental stages of C. millsae are shown in photographs and terminology of brooding and viviparity is discussed relative to other Cnidaria.