Enoplochiton niger (Barnes, 1824)

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

Enoplochiton niger (Barnes, 1824) Plate 2, Fig. 1; Table 2

Chiton niger Barnes, 1824: 71, pl. 3, fig. 3. Enoplochiton niger : Pilsbry 1893: 14: 252, pl. 52, figs 22-29; Marincovich 1973: 43, fig 99. Acanthopleura nigra : Ferreira 1986: 266, figs 106-111 and 113-N.

Description.

Animal very large in size, up to 190 mm in examined specimens. Tegmentum dark chocolate-brown, shiny, but easily eroded. Anterior valve with 4-6 concentric, zig-zagged furrows. Lateral areas elevated, well defined by strong round rib at diagonal line, with zig-zagged furrows as on anterior valve. Central areas well defined, smooth jugum bordered by narrow, depressed area with irregular, short, oblique furrows; para-jugal area smooth; pleural area with longitudinal, parallel furrows, not usually reaching anterior border of valve. Girdle thick, muscular; dorsal surface dark brown, conspicuously dotted with light brown scales, scales irregular in size (larger in middle 1/3 of girdle), up to 1.5-2 mm long in specimens 50 mm long (larger in larger specimens), vaguely striate, usually eroded at upper edge, clearly separated from each other by area as wide as scale; on outer 1/5 of girdle, scales much smaller, shorter, dark brown, erect, spine-like; girdle surface completely covered otherwise with minute, dark brown, lanceolate spicules, up to 100 μm long, 25 μm thick. Girdle bridges, empty in middle third, but crowded with small, dark brown spiculoid elements (akin to those on girdle proper) in outer thirds (After Ferreira 1986).

Material examined.

Specimens found exposed on large boulders in the surf–zone, in Playa Rodillo, Playa El Pulpito (MPCCL 3072014E, 1 specimen) and in Norte Bahía de Caldera.

Distribution.

This species is confined to the western temperate coast of South America, from Talara, Peru (04°34'S; 81°16'W) to Coquimbo Bay, Chile (29°57'S; 71°20'W). Its bathymetric range is limited to the intertidal zone ( Ferreira 1986).

Remarks.

With sizes up to 200 mm ( Sanhueza et al. 2008), this is one of the largest polyplacophoran species in the country. It lives almost exclusively in exposed rocks or in the surf zone. Although this species is mostly herbivore, it has been described also as a generalist polyphagous consumer, and a potential omnivorous, ( Sanhueza et al. 2008). A brown-colored variety of the limpet species, Scurria variabilis (Sowerby, 1839), lives on the valves of this species, having been found in all the specimens examined in this study. An unidentified barnacle was also observed on the valves of a few specimens. In some places (Rodillo beach, Obispito bay; Table 1) juvenile specimens can be found among crevices of large boulders. It was observed that this species is predated by the common gull, Larus dominicanus (Lichtenstein, 1823), an omnivore species that also predates on the intertidal large keyhole limpets of the genus Fissurella (Bahamondes & Castilla, 1986).