The life cycle of Halimedusa typus, with discussion of other species closely related to the family Halimedusidae (Hydrozoa, Capitata, Anthomedusae)

Abstract

The little-known Anthomedusa Halimedusa typus has been collected from several locations in California, Oregon, and British Columbia on the Pacific coast of the United States. The adult medusa is redescribed based on new observations of living material and is found to have capitate tentacles. Polyps of H. typus were raised several times after spawning field-collected medusae in the laboratory; the cultures on one occasion lived for more than a year. The capitate polyp is solitary and very tiny, emerging from a basal perisarc measuring 200-300 µm in diameter. One cultured polyp produced a medusa, which is described. The taxonomic positions of several other morphologically-similar Anthomedusae in the Capitata are compared and discussed here. Tiaricodon coeruleus and Urashimea globosa are moved from the Polyorchidae to the Halimedusidae, and the similarity of Boeromedusa auricogonia (Boeromedusidae) to all of these medusae and to the genera Polyorchis, Scrippsia and Spirocodon of the family Polyorchidae is considered. The group of species under consideration is basically restricted to the Pacific Ocean, except for T. coeruleus and U. globosa, which have also been collected in the south Atlantic and south Atlantic/Antarctic. It is noted that medusae of the Halimedusidae are typically found quiescent near the surface, whereas those of the Polyorchidae either rest on the bottom or must continue pulsating to stay up in the water column, indicating a basic underlying difference in buoyancy and resultant behavior between the medusae in these two families.