Callistochiton elenensis

Callistochiton elenensis (Sowerby in Broderip & Sowerby, 1832)

(Figures 2I, 7G–K)

Chiton elenensis Sowerby in Broderip & Sowerby, 1832: 50–61. Chresonymy and synonymy in Kaas & Van Belle (1994).

Type material. Lectotype, designated by Kaas & Van Belle (1994), NHM 20150526.1 (the left specimen on the tablet) from the H. Cuming collection. Acc. no: 1829/1.

Type locality. Santa Elena, Panamá.

Material examined. Eleven specimens, BL 5.7–14.5 mm.

Habitat. In the intertidal on medium–sized and small semi–humid rocks. At Las Palmas and Playa Pintas, the rocks were densely covered with the algae Dictyosphaeria decaisne.

Remarks. Callistochiton elenensis has a sculpture of wide, thick, elevated ribs with rounded knobs (Figs. 7G– I). Dorsal girdle scales 3 times wider than long with 10–12 wide, longitudinal ribs (Fig. 7J). Major lateral radular tooth tricuspid, minor lateral tooth smaller and shorter than the central tooth, which appears as an elongated plate (Fig. 7K).

According to Ferreira (1979), Kaas & Van Belle (1994) and García-Ríos & Álvarez-Ruiz (2007), Callistochiton elenensis shows a distribution range from Pichilingue, Balandra and Tecolote, La Paz, Baja California Sur (BCS) to Punta Ancón, Santa Elena peninsula, Ecuador. In the Mexican Tropical Pacific (MTP), the species has been recorded in Mazatlán, Sinaloa and Sayulita, Nayarit, as a common member of the rocky intertidal (Flores-Garza et al. 2012; Galeana–Rebolledo et al. 2014; Reyes–Gómez et al. 2010; Reyes–Gómez et al. 2022). Ríos–Jara et al. (2020) also recorded this species from Bahía de Chamela, Jalisco.

This is a medium–sized species (up to 21 mm); it is characterized by radial ribs on the lateral areas of the head and tail valves. The ribs are formed by pustules or slightly elevated rounded nodules and a net–like sculpture on the central areas. The detailed study of specimens from La Paz (BCS), Sayulita (Nayarit) and Acapulco (Guerrero) performed by Reyes–Gómez et al. (2022) revealed that the specimens from the southern coasts of México are smaller (up to 14 mm) and have fewer radial ribs on the head and tail valve (8) than the specimens from La Paz. The specimens examined by us have a head valve with nine thick radial ribs, eight ribs on the tail valve and a maximal size of 14.5 mm. The specimens obtained from Bahía San Carlos, Puerto Peñasco, Sonora and from Bahía de los Ángeles have a similar size as those from the MTP. They also display nine ribs on the head valve and eight on the tail valve. Their tegmentum sculpture is less elevated and not as coarse.