Crossota millsae (Cnidaria: Trachymedusae: Rhopalonematidae), a new species of viviparous hydromedusa from the deep sea off California and Hawaii

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.

Morphological variation among populations of an invasive jellyfish

“…A large literature indicates that cnidarians are no exception to this phenomenon and are indeed renowned for exhibiting high levels of developmental phenotypic plasticity (e.g. Hincks 1868, Merejkowsky 1883, Van Beneden 1884, Schmid 1974, Bavestrello et al 1992, Boero et al 1996, Bavestrello et al 2000, Schroth et al 2002, Thuesen 2003. The extent to which scyphozoans exhibit phenotypic morphological variation in response to new environmental conditions is, however, unknown.…”

The Gelatinous Macroplankton Community at the Hatoma Knoll Hydrothermal Vent

“…10, 3,668 m depth, 14:21, 8 Jun 2000, off Hawai'i, California (2,540 m and 3,244 m depth) and in the Sea of Cortez (Thuesen 2003), as well as from depths between 1,614 and 2,093 m in the Chukchi Basin, Arctic Ocean . During the present study it was observed at 1,440 m depth during ROV HyperDolphin dive 296. perradial manubrial pouches, oval in outline, usually somewhat longer than wide, septa between them alternating with tentacle roots; 20-40 marginal tentacles, stiff, tapering, up to slightly longer than diameter of umbrella; no peripheral canal system; gonads?…”

Two swimming modes in Trachymedusae; bell kinematics and the role of giant axons

“…On this occasion, the animal travelled three body lengths. The size of the animal was not recorded but the species has been described as being up to 28 mm wide ( Thuesen, 2003 ). Its orientation was such that changes in bell height and diameter could be measured sufficiently accurately to reveal a significant delay in the onset of contraction in the mid-bell region.…”