Abstract: A new hydromedusa has been discovered off the coast of Tahiti in the waters of French Polynesia. The species belongs to the genus Eutiara, which prior to this study included two valid species. The third species described in this paper can be differentiated based on the specific form of the umbrella and its extensions of the tentacle bulbs, characteristic of the family Pandeidae as described by Russell (1953), Kramp (1959,1961) and Bouillon et al. (2006). Long exumbrellar spurs extending above the tentacle bulbs are typical of the genus Eutiara but the eight tree-like ramified ribs, extensions of the exumbrellar spurs, which nearly cover the exumbrella, seem to be specific to this new species, Eutiara decorata.
Keywords: jellyfish, new species, Eutiara, Tahiti, Pacific Ocean, French Polynesia, Pandeidae, Cnidaria
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Jellyfishes are a conspicuous component of the macroplankton biomass of the Pacific Ocean but there are no recent reviews of the jellyfishes of French Polynesia, situated in the tropical and subtropical South Pacific Ocean. Tahiti is the main island of French Polynesia; the medusae of the Tahitian waters are currently being studied (in preparation) and among them is a new species, which appeared to be a Pandeidae, belonging to the genus Eutiara as described by Bigelow in 1918. In the 1918 original publication, Bigelow proposed the genus Eutiara as follows "It may be defined as Pandeidae with blind centripetal canals alternating with the radial canals; with well-developed mesenteries; complex gonads fundamentally of the 'Neoturris' type." Reports of hydroids from the South Pacific Ocean date as far back as the early 19th century by Ernst Haeckel (1879); however, there have been no comprehensive faunistic account of the group in this area recently.
Hydrographically, the area is interesting, as the waters around the islands are very deep just beyond the coral reef surrounding most islands, and the water temperatures on the surface vary little during the year (between 25 and 30 [degrees]C). Thanks to the size of the jellyfishes, most of them are easily observable by divers or manned submersibles. The present observations, made in situ by scuba diving throughout the year offshore Tahiti, show the different stages of development during a lifetime of several months, as is the case for other species in this family.
MATERIALS AND METHODS
An account is given here of the new species from Tahiti. All 35 of the specimens seen so far have been collected or observed and photographed at night, in the wild state, off the island of Tahiti, in the pelagic zone at a distance ranging from 1 to 4 km from the barrier reef extending around Tahiti Island. The bottom in this area ranges from 800 m to more than 2,000 m deep. The geographic coordinates provided are shown in Table 1. All sightings of this species have been made while scuba diving between 2 and 4 hours after sunset. The water temperature from the surface down to at least 50 m deep was between 26 and 29 [degrees]C. The specimens were observed at...