Callistochiton pulchellus (Gray, 1828)

Araya, Juan Francisco & Araya, Marta Esther, 2015, The shallow-water chitons (Mollusca, Polyplacophora) of Caldera, Region of Atacama, northern Chile, Zoosystematics and Evolution 91 (1), pp. 45-58 : 45

Taxon classification Animalia Chitonida Callistoplacidae

Callistochiton pulchellus (Gray, 1828) Plate 1, Fig. 2; Table 2

Chiton pulchellus Gray, 1828: 6, pl. 3, fig. 9. Chiton bicostatus d’Orbigny, 1847: 486, pl. 81, figs 7-9. Callistochiton shuttleworthianus : Bergenhayn 1937: 284, figs 3 f–g (non Callistochiton shuttleworthianus Pilsbry, 1893). Callistochiton carmenae Smith & Ferreira, 1977: 87, figs 10-11. Callistochiton pulchellus : Ferreira 1979: 460, figs 25-26; Aguilera 2005a: 207, fig. 1. Detailed bibliography and synonymy in Kaas and Van Belle (1994: 161).

Description.

Animal of small size, up to 11.5 mm in examined specimens, elongate oval, moderately elevated, color of tegmentum creamy white or bright white. Head valve semicircular, sculpture with 10-15 low rounded, equally spaced, nodulose, annulate, radial ribs, becoming obsolete towards the apex, the posterior ribs being strongest and more nodulose. Intermediate valves rectangular, lateral areas well defined, sculptured with two strong radial ribs. Central area with two series of equally spaced, diagonal lirae, forming rounded depressions in the interspaces. Tail valve semi-oval, slightly less wide than head valve, sculptured like head valve, with 8-11 weaker radial ribs. Girdle rather wide, yellowish white, dorsally covered with small, oval, imbricating scales (After Kaas and Van Belle 1994).

Material examined.

Specimens found under sunken rocks in tidal pools in Playa El Pulpito (SBMNH 452240, 1 specimen), Sur de Playa Ramada and Playa El Pulpo (Table 1).

Distribution.

This species has records from Islay (17°03'S; 72°06'W), Peru to Chanavayita cove, 54 km south of Iquique, Chile (20°42'S; 70°09'W), with records also in the Galápagos Islands (01°40'N; 92°01 W), Ecuador ( Aguilera 2005a). The present record (at 27°S) is now the southernmost record for this species.

Remarks.

This is a small (under 12 mm) chiton, easily overlooked but for its bright whitish color. It is a fairly rare species; they were not abundant and were found only in two of the studied locations (Table 1), under rocks sunken in tidal pools, associated to small communities of Acar pusilla Sowerby, 1832, Liotia cancellata Gray, 1842, Rissoina inca Sowerby, 1832, encrusting algae and sponges. It has been reported that this species feeds on sponges, bryozoa and diatoms ( Aguilera 2005). This species can be mistaken for Calloplax vivipara (Plate, 1902), differing from this species in having a less elongate body shape, with a much finer and subtle sculpture (especially noticeable on the terminal valves), it differs from Calloplax vivipara in having rounded depressions in the central-lateral areas of the valves, especially in the middle valves.