Inventory of chiton species (Polyplacophora) from the rocky intertidal of the Northern Gulf of California, with an illustrated taxonomic key Author Reyes-Gómez, Adriana Doctorado en Biosistemática y Manejo de Recursos Naturales y Agrícolas. Author Vargas-Ponce, Ofelia Departamento de Botánica y Zoología. Author Galván-Villa, Cristian Departamento de Ecología Aplicada, Centro Universitario de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, Camino Ing. Ramón Padilla Sánchez 2100, Zapopan, Jalisco, 45200, México. Author Salgado-Barragán, José Laboratorio de Invertebrados Bentónicos, Unidad Académica Mazatlán, Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, México. Author Esqueda-González, Ma. Del Carmen Departamento de Ecología Aplicada, Centro Universitario de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, Camino Ing. Ramón Padilla Sánchez 2100, Zapopan, Jalisco, 45200, México. Author Ríos-Jara, Eduardo Departamento de Ecología Aplicada, Centro Universitario de Ciencias Biológicas y Agropecuarias, Universidad de Guadalajara, Camino Ing. Ramón Padilla Sánchez 2100, Zapopan, Jalisco, 45200, México. text Zootaxa 2023 2023-05-26 5296 2 147 178 http://dx.doi.org/10.11646/zootaxa.5296.2.2 journal article 10.11646/zootaxa.5296.2.2 1175-5326 7973065 624273A6-3028-42C2-ABE2-A18BBF828156 Nuttallina crossota ( Berry, 1956 ) ( Figures 3C , 9A–I ) Nuttallina crossota Berry, 1956: 71–74 . Chresonymy and synonymy in Ferreira (1982) . Type material. Holotype , SBMNH 34423 from the “Berry collection 15133”. Type locality. Puerto Peñasco , Sonora , México . Material examined. Forty-one specimens, BL 8.5– 7.1 mm . Habitat. In the upper intertidal on medium–sized and small rocks, on exposed rocky massifs, among brown algae that were also under large rocks buried in sand. Remarks. Nuttallina crossota exhibits irregular granulose sculpture arranged in quincunx ( Figs. 9A–D ); the lateral areas are reduced with 2 elevated thick radial ribs ( Figs. 9B, C ); jugal area with the sculpture, however, usually very much eroded in adult specimens ( Figs. 9B, C ). Girdle densely covered with small elongated, striated spicules and interspersed, thick hyaline spicules ( Figs. 9E–F ). Major lateral radular tooth tricuspid, minor lateral reduced, smaller and shorter than central tooth; central tooth appears as a sub–rectangular plate with its apical edge slightly bent outwards ( Figs. 9H–I ). The genus Nuttallina was considered a member of the family Callistoplacidae (Pilsbry 1893; Smith 1960 ) due to the similarity of the insertion slits of the articulamentum and the ribs of the valve tegmentum. Later, this genus was included in the family Lepidochitonidae (see Thiele 1929 ; Thorpe 1971 ; Van Belle 1977 ) based on four characteristics: 1) the tegmentum has granules, 2) the tail valve is smaller than the head valve, 3) the major lateral tooth is tricuspidate, and 4) the girdle scales are small. Nuttallina crossota is endemic and the only species of this genus in the Gulf of California . At Puerto Peñasco (the type locality), the species was not found, while at Playa Cementerio , the number of the collected individuals was three and at Las Palmas , Bahía Kino two specimens were found. However , at Pie de Faro , Bahía San Felipe , the number of individuals collected was high (36 individuals). Most of the individuals showed an eroded tegmentum on the jugal area of the intermediate valves; some were eroded in the lateral areas as well. At Pie de Faro , Bahía San Felipe , the specimens were found sheltered among brown algae densely covering a large volcanic rock massif with a rough surface, 1.60 m high and 12 m long. During low tide, the rock massif was totally exposed and dry with Nuttallina crossota covered by the algae. In the lower part of the beach, they were observed on (large) submerged rocks semi–buried in sand and buried on the base of the rock massif.