Accepted by J. Svavarsson: 23 Sept. 2008; published: 17 Oct. 2008 51 ZOOTAXA ISSN 1175-5326 (print edition) ISSN 1175-5334 (online edition) Copyright © 2008 · Magnolia Press Zootaxa 1908: 51–56 (2008) www.mapress.com/ zootaxa/ New Zealand exports: Pseudosphaeroma Chilton, 1909 (Isopoda: Sphaeromatidae), a Southern Hemisphere genus introduced to the Pacific coast of North America NIEL L. BRUCE 1 & REGINA WETZER 2 1 Museum of Tropical Queensland and School of Marine and Tropical Biology, James Cook University, 70-102 Flinders Street, Towns- ville, 4810, Australia. E-mail: niel.bruce@qm.qld.gov.au 2 Natural History Museum of Los Angeles County, 900 Exposition Blvd., Los Angeles, CA 90007, USA. E-mail: rwetzer@nhm.org Abstract Collections made along the coast of California have revealed the presence of a species of Pseudosphaeroma Chilton, 1909, a genus common in New Zealand coastal waters. The genus is entirely Southern Hemisphere in distribution, and this record reports the introduction of a species of Pseudosphaeroma into the San Francisco and Central Coast region of California, the first reported occurrence of the genus as an invasive taxon, and the first record of the genus from the Northern Hemisphere. The genus is also recorded for the first time from the Galapagos and Argentina. Key words: California, Isopoda, Sphaeromatidae, Pseudosphaeroma, New Zealand Introduction Pseudosphaeroma Chilton, 1909 is a small genus of Southern Hemisphere sphaeromatid isopods, most recently reviewed by Harrison (1984). A diagnostic and unique character of this genus is the upturned apex to the posterior margin of the pleotelson in males, and the uropodal exopod is distinctly shorter than the endo- pod. Harrison (1984) placed three species into the genus, and excluded a further three species, these lacking the diagnostic upturned pleotelson. The species are the type species Pseudosphaeroma campbellense Chilton, 1909, a species purportedly commonly encountered around New Zealand; Pseudosphaeroma lundae Menzies, 1962, which occurs on the Chilean coast between Coquimbo and Archipiélago do los Chanos (c. 30–45°S); and Pseudosphaeroma tuberculatum (Sivertsen & Holthuis, 1980), described from Tristan da Cunha. This discovery of a species of Pseudosphaeroma in Californian harbours has, again (e.g. see Poore 1996 in response to Chapman & Carlton 1991, 1994), highlighted the need for sound and rigorous taxonomy in order to be able to identify marine organisms that may or may not have been introduced by trans-oceanic ship- ping. The common New Zealand ‘species’ that has been recorded under the name Pseudosphaeroma campbel- lense appears to be at least three species, and all other records of that species have to be considered as doubtful. The species from San Francisco Bay does appear to be one of the common New Zealand species, but is not a named species. Given the known Southern Hemisphere distribution of the genus, the abundance of Pseudosphaeroma species in New Zealand, its occurrence only in San Francisco harbour and Morro Bay in the United States, we are confident that the species has been introduced to California. Only one isopod species is believed to have been translocated from New Zealand — Eurylana arcuata (Hale, 1925), which has been introduced to Australia and San Francisco (Bruce, 1986, Bowman et al., 1981). Unless otherwise stated material is held at: Natural History Museum of Los Angles County, California