Introduction The most well-known members of the ocean’s gelatinous fauna are arguably the scyphomedusae. Mass occurrences of members of this group, including the moon jellyfish Au- relia aurita and the giant jellyfish Nemopilema nomurai (Omori & Kitamura 2004), can seriously interfere with man’s economic activities, such as trawl fisheries, fixed-net fisheries, and electric power plants (Shimomura 1959; Mat- sueda 1969; Yasuda 1982, 1988). Over the last few decades, although many ecological studies concerning jellyfish blooms have been carried out, the species targeted in these studies are all shallow water species (Purcell et al. 2001). Studies on scyphomedusae (Youngbluth & Båmstedt 2001; Miyake et al. 2002; Matsumoto et al. 2003; Lindsay et al. 2004) and other gelatinous zooplankton (Larson et al. 1991; Larson et al. 1992; Mills et al. 1996; Toyokawa et al. 1998; Wrobel & Mills 1998; Hunt & Lindsay 1999; Miyake et al. 2001) using submersibles have increased in recent years. Mass occurrences of jellyfishes have been reported in deep waters off Hokkaido, Japan. Toyokawa et al. (2003) re- ported dense aggregations of the lobate ctenophore Bolinopsis infundibulum at 1250 m depth, and Miyake et al. (2002) reported aggregations of Aurelia limbata at 250–450 m depths. Parumbrosa polylobata Kishinouye, 1910 (Scyphozoa; Semaeostomae; Umbrosinae) has been reported from rela- tively deep water in Toyama Bay, Sea of Japan, near the Goto Islands chain at the southernmost lip of the Sea of Japan and from Indochina (Kishinouye 1910; Bigelow 1913; Uchida 1936, 1954; Ranson 1945; Kramp 1961). This species was caught in a shrimp trawl net from deep water (130 m depth) and has never been found at the sur- face in Japanese waters (Kishinouye 1910). Except for one example in Ranson (1945), the reported distribution of this species has until now been restricted to along the coast of the Sea of Japan. No ecological data are presently available for this species, and there have been no additional data con- cerning it since Uchida (1936). In the present study, dense aggregations of P. polylobata were observed in the deep sea in Suruga Bay, along the Pa- cific coast of Japan. In Japanese waters, this is the first record of P. polylobata outside the Sea of Japan. Ecological data concerning P. polylobata (habitat environment, occur- rence time, distribution pattern, swimming behavior in situ Occurrence of the Scyphomedusa Parumbrosa polylobata Kishinouye, 1910 in Suruga Bay, Japan HIROSHI MIYAKE 1,3 *, DHUGAL J. LINDSAY 1 , MINORU KITAMURA 1 & SHUHEI NISHIDA 2 1 Marine Biology and Ecology Research Program, Extremobiosphere Research Center, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2–15 Natushima-cho, Yokosuka 237–0061, Japan 2 Department of Marine Ecosystems Dynamics, Ocean Research Institute, University of Tokyo, 1–15–1 Minamidai, Nakano-Ku, Tokyo 164–8639, Japan 3 Enoshima Aquarium, 2–19–1 Katase-Kaigan, Fujisawa city, Kanagawa 251–0035, Japan Received 12 March 2004; Accepted 13 January 2005 Abstract: Aggregations of the scyphomedusa Parumbrosa polylobata were observed in the deep sea of Suruga Bay, Japan, using a crewed submersible and ROVs. This is the first record of P. polylo- bata off the Pacific coast of Japan. Parumbrosa polylobata was distributed in the benthopelagic layer (within 50 m of the seafloor) at 270–510 m bottom depth and was an active swimmer that was ob- served to feed on gelatinous zooplankton. Medium microbasic euryteles, one of four nematocyst types observed in the medusae, may play an important role in capturing gelatinous prey. Moribund individuals sank to the seafloor and became food for the benthos. Parumbrosa polylobata, which oc- curred in dense aggregations in the benthopelagic layer, seems to play an important role in matter transport from the pelagic to benthic communities. Key words: scyphomedusa, Parumbrosa polylobata, Suruga Bay, nematocyst, benthopelagic layer Plankton Biol. Ecol. 52 (1): 58–66, 2005 plankton biology & ecology © The Plankton Society of Japan 2005 * Corresponding author: Hiroshi Miyake; e-mail, miyake@enosui.com; TEL: +81–466–29–9967; FAX: +81–466–29–9974