111 down to Central America, Guatemala, Salvador, Hon- duras and Nicaragua (Ramirez-Luna & Barrientos-Lu- ján, 1999). Here we present the irst study on chitons from a coral- line region at the Mexican Tropical Paciic, providing data on their distribution in the area. Material and methods The specimens were collected in living and dead coral- line areas and rocky shores of Oaxaca, from several sites within this area and along 145 km of coast, between Ba- choco beach and the Copalita River. Eight collecting sites were studied: Puerto Escondido (Puerto Angelito), Bahías de Huatulco (Casa Mixteca, Chachacual-Jicaral, Cacaluta) and Puerto Ángel (Estacahuite) (Fig. 1). The specimens were obtained from semi-monthly samplings (every-other month) during 1994 and 1995; in addition, we also included material collected in sporadic sam- plings within the same area from 1999 to 2008. This habitat displays a high diversity of algae and in- vertebrate species and it is characterized for its rocky- coralline bottom substrate, composed by living and dead coral heads with up to 5 m of height, down to a depth of 14 m. The main coral genus is Pocillophora, Introduction The study of chitons in Mexico has been raised in the last two decades; the latest works are about Chiton (C) articulatus (Flores-Campaña et al., 2006) and its popula- tion structure from Pájaro and Venados Island in Maz- atlán, and the study about chitons of La Paz (Garcia- Rios, 2007). Both contributions represent an excellent effort to generate new studies. Although there are other areas where exploration is needed, besides the over ex- plored Baja California Peninsula and the Gulf of Cali- fornia, this is the case of the Mexican Tropical Paciic. It is a fact that in Mexico there are habitats of special interest, due their fragility, closeness and exposure to urban areas, like the reefs and shores of Oaxaca, where the expeditions and collecting campaigns have been few or almost null. This coralline reef system is located in the Mexican Tropical Paciic, at the western coast to- wards the very south of México (Fig. 1). This area com- prises the distant Tropical Eastern Paciic, with smaller wealth of coral species, since it counts on around 50 species, whereas in Indo-Paciic 500 species are record- ed (Glynn & Leyte-Morales, 1997). This system is com- posed by 26 coralline formations and this particular re- gion is isolated from other coralline areas like those at the North of México at Guerrero, Michoacán and far Boll. Malacol., 46: 111-125 (2/2010) Chitons from the coralline area of Oaxaca, Mexico (Polyplacophora) Adriana Reyes-Gómez* (), Norma A. Barrientos-Lujan*, Jorge Medina-Bautista* & Silvia Ramírez-Luna* * Universidad del Mar, UMAR, Oaxaca, México; Laboratory of Marine Ecology, quitonreyes@yahoo.com () Corresponding author Abstract The polyplacophoran fauna from the rocky-coralline system of Oaxaca, in the Mexican Tropical Pacific, consists of 13 species, including either endemic and widely distributed species. Chitons were collected in eight localities along the central area of Oaxaca, at 0-7 m of depth. Lepidochitona (L.) salvadorensis is recorded for the first time from Mexican waters. New data of distribution are reported for Lepidozona (L.) serrata, Stenoplax (S.) mariposa and Acanthochitona arragonites all previously known only from the Gulf of California. Chiton (C.) albolineatus is confirmed as an endemic species of the Mexican Tropical Pacific. Two species, Lepidochitona sp. and Ischnochiton sp., are probably new and will be described when more material will be available. Each species is systematically treated, commented and illustrated. Riassunto Negli ambienti di natura roccioso-corallina di Oaxaca, nel Pacifico Tropicale del Messico, sono state indivi- duate 13 specie di chitoni. Sono presenti sia elementi endemici, sia elementi ad ampia distribuzione geo- grafica. I chitoni studiati provengono da otto località nel settore centrale di Oaxaca, e sono stati raccolti a profondità di 0-7 m. Lepidochitona (L.) salvadorensis, in precedenza nota solo per El Salvador, viene segna- lata per la prima volta in acque messicane. Nuovi dati di distribuzione vengono riportati anche per Lepido- zona (L.) serrata, Stenoplax (S.) mariposa e Acanthochitona arragonites, tutte note in precedenza solo per il Golfo di California. Chiton (C.) albolineatus risulta essere una specie endemica del Pacifico Tropicale del Messico. Vengono segnalate due specie, Lepidochitona sp. ed Ischnochiton sp., probabilmente nuove ed in attesa di essere descritte sulla base di materiale supplementare. Tutte le specie ritrovate sono trattate sistematicamente ed illustrate. Key words Polyplacophora, Mexico, Oaxaca, systematic, distribution.