Radsia barnesii (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 Chitonidae

Radsia barnesii (Gray, 1828) Plate 1, Fig. 2; Table 2

Chiton barnesii Gray, 1828: 5; Reeve 1847: pl. 1, sp. 1. Chiton (Radsia) barnesii : Pilsbry 1893: 190, pl. 29, figs 10-12; Dall 1909: 247. Chiton barnesii : Plate 1899: 59, pl. 4, fig. 191; Leloup 1956: 46. Radsia barnesii : Bullock 1988: 282, figs 2,4,6,7, 11-13, 15, 31, 32. A more complete synonymy in Bullock (1988: 282)

Description.

Animal of medium size, reaching a length of 28 mm in the examined specimens. Anterior valve straight; post-mucronal slope of posterior valve straight to slightly concave. Valves quite flat. Jugal region smooth; central area with numerous uneven longitudinal ribs. Lateral triangle barely raised, with 5-7 irregular nodules. Shell color cream white with reddish brown splotches on central areas, irregular longitudinal dark reddish brown bands on lateral triangles, and occasional dark reddish brown on jugum. Girdle light greenish brown with faint trace of alternating lighter bands in some specimens. Interior of valves white (After Bullock 1988).

Material examined.

Specimens found in three locations; Peninsula Calderilla, Sur de Playa Ramada and in Playa El Pulpo Beach (Table 1). Collected under rocks and rock slabs, Peninsula Calderilla (MZUC 39614, 1 specimen).

Distribution.

Bullock (1988) cites this species from Coquimbo (29°58'S; 71°21'W), to the Chonos Archipelago (45°0 ’0” S; 74°0 ’0” W), Chile. The present record (at 27°S) is now the northernmost record for this species.

Remarks.

This species was uncommon in the zone under study; only a few specimens were found in the undersides of rocks at low tide. This species is clearly identified from the other species found in this work by having a wide, flat shell, with narrower valves and a pattern of clear and darker alternating bands in the girdle. It can be misidentified as Chiton granosus ; differing from this species in the smaller size, the much smaller girdle scales, a much weak valve sculpture and in the alternating bands of the perinotum, absent in Chiton granosus .