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...Maria Madre islands, and from dead coral substrates from Socorro Island. All previous records of Annelid Polychaetes from the study area were also included; 348 species are now recorded from 36 islands in the Mexican Pacific. The highest number of species is recorded from Espiritu Santo Island (56 species) in the region of the Gulf of California and Maria Madre and Socorro islands (69 and 70 species) in the central Mexican Pacific.

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The islands have always been considered a natural biological laboratory and have, as such, focused the attention of ecologists and evolutionists in their attempt to define if the species present are consistent with local geological records; the study of the biological processes in those isolated habitats has even been at the heart of setting forth theories such as the equilibrium theory in island biogeography (MacArthur and Wilson 1967).

In the Mexican Pacific, between latitudes 14[degrees]45' and 32[degrees]26' N, more than 140 islands and islets are found, but their polychaete fauna is largely unknown: the majority of the records are the product of sporadic or fortuitous collections. Research on polychaetes from these islands has been basically done by Rioja (1960, 1962) in several Pacific islands, Salazar-Vallejo et al. (1987), Gongora-Garza (1984), and Gongora-Garza and De Leon-Gonzalez (1993) in Maria Madre Island and Salazar-Vallejo (1990) in Rasa Island; occasional records have been done in the vicinity of some islands by Treadwell (1914, 1929, 1937, 1941), Chamberlin (1919), Moore (1923), Hartman (1939a, b, 1940, 1941, 1944a, 1944b, 1950), Berkeley and Berkeley (1939, 1958), Steinbeck and Ricketts (1941), Rioja (1941, 1947a, 1947b, 1947c), Fauvel (1943), Fauchald (1968, 1970, 1972, 1982, 1992), Pettibone (1971), Sarti-Martinez (1984), De Leon-Gonzalez (1985), Bastida-Zavala (1990), Holguin-Quinones et al. (1992), Holguin-Quinones (19 94), and Bautista-Romero et al. (1994). These records together with the material obtained for this study make up for 348 species in littoral and sublittoral habitats from areas adjacent to the islands of the Mexican Pacific.

The Polychaetes are the best represented taxonomic group in the benthic communities, be it in hard or soft bottoms (Mackie and Oliver 1996), where they can reach between 36% and 70% of the total fauna, and between 25% and 65% of the species present. For this reason, their distribution patterns frequently reflect those of the whole benthic fauna (Blake 1994; Mackie et al. 1997; Glasby and Read 1998). Being such a diversified and ubiquitous group, they can increase considerably the biodiversity values of any habitat considered. In this case, the description of the communities found around the islands located in the Mexican Pacific and Gulf of California is necessary, not only because of the great number of islands present, but also because several of them have been declared priority areas by the Mexican government, so that specific strategies are being implemented for their protection and management (SEDESOL 1994), all of which is impossible without a basic knowledge of the biota present.

The purpose of this study, then, is to synthesize the results of previous records as well as to add to the knowledge of this group, with the results of the identifications of the polychaetes collected by us in Tiburon, Del Carmen, Maria Madre and Socorro islands. We include a systematic list with all the records made around the islands of the Mexican Pacific as well as their affinities according to their faunistic composition.

Methods

Samples were collected in March 1985 in soft bottoms in four sublittoral stations (29-102 m) from Tiburon, Del Carmen and Maria Madre islands, as part of the expedition "Cortes"; and in November 1997, in dead coral substrates from seven localities (0.40 to 20.5 m) in Socorro Island, Revillagigedo as part of the expedition "Surpaclipp" (Fig. 1).

The soft bottom samples were collected with a Smith-McIntyre (0.1 [m.sup.2]) dredge, and those from hard bottoms manually, either directly or with SCUBA diving techniques. Fixation of the organisms was done with 10% formaldehyde followed by preservation in 70% ethanol. The polychaetes were identified and deposited in the "Coleccion de Poliquetos del Instituto de Ciencias del Mar y Limnologia, Universidad Nacional Autonoma de Mexico" (CP-ICML, UNAM; DFE.IN.061.0598).

The previous records herein reported are taken from the existing literature, following an exhaustive revision. Outdated terminology was corrected in favor of presently valid names, based on the publications by Reish (1968), Salazar-Vallejo (1989) and Hernandez-Alcantara (1992), since these are the basic studies about polychaetes from the Gulf of California and the Mexican Pacific.

Results and Discussion

The comprehensive list of the 348 species of polychaetes so far identified from Mexican Pacific islands is shown in Table 1, which includes also the 96 species identified for this study. The species which were found to be first records for the particular areas are also indicated. In Table 2, the number of species so far recorded for all the islands (including our survey), are shown, divided by state. The taxonomic arrangement follows Rouse (2000).

For this study, 1375 specimens belonging to 96 species of 29 families were identified from the islands of Tibur6n, del Carmen, Maria Madre and Socorro. The scant knowledge of the polychaetes living in the islands of western Mexico is evidenced by the fact that between 48% and 89% of the species identified in this survey are registered for the first time in each island (Table 1). From soft bottoms (fine...

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