Chiton (Chiton) granosus Frembly, 1827

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

Chiton (Chiton) granosus Frembly, 1827 Plate 1, Fig. 6; Table 2

Chiton granosus Frembly, 1827: 200, suppl. pl. 17, fig. 1; Plate 1902: 56, pl. 4, fig. 190; Pilsbry 1893: 167, pl. 30. figs 27, 28; Dall 1909: 247. Chiton (Chiton) granosus : Marincovich 1973: 43, fig. 98. Chiton (Chondroplax) granosus : Bullock 1988: 185, figs 96, 97, 103, 140, 141, 143, and 144; Osorio 2002: 56.

Description.

Animal of large size, up to 45 mm in examined specimens. Intermediate valves often eroded and rather flat. Anterior valve convex, post-mucronal slope straight. Mucro moderately blunt; centrally located on posterior valve. Jugal tract smooth, central areas with somewhat beaded longitudinal ribs. Lateral triangle barely raised; low, broad, nodular rib extends along diagonal line. Often a few other radiating rows of nodules appear on lateral triangle. Terminal areas with 10-12 radiating rows of widely spaced nodules. Color of tegmentum nearly totally dark brown to greenish brown, with occasional streaks of cream white on jugal and central areas. Girdle black. Interior of valves white with dull blue muscle scars and reddish brown on posterior slope of callus (After Bullock 1988). According to Osorio (2002) this species is gonochoric, like almost all other chiton species that have been studied. It can reach a maximum length of 80 mm.

Material examined.

Specimens found in Playa El Pulpo, Norte de Bahía de Caldera, Playa Mansa and Sur de Bahía de Caldera, in crevices in large rocks, often in surf zone in large colonies. Playa el Pulpo (MPCCL 3072014D, 1 specimen).

Distribution.

Marincovich (1973) gives the northernmost distribution for this species at Paita (05°05 ’34” S; 81°06 ’07” W), Peru. Osorio et al. (2005) records the southernmost record of this species at Boca del Guafo (43°39'S; 74°00'W), Region of Aysén, southern Chile.

Remarks.

This species is somewhat uncommon in shallower waters; it is found mostly in crevices and in rocky outcrops, mostly in clustered distributions. Juvenile specimens are somewhat similar to the juvenile specimens of Chiton cumingsii differing in the paler coloration (of various shades of green), the granulation on the valves and in the overall wider body. It has been reported that this species feeds on barnacle cyprids ( Moreno and Jaramillo 1983, Aguilera 2005) and is preyed on by the common gull Larus dominicanus (Lichtenstein, 1823). It was observed also that some specimens had barnacles on the valves. This species is a physiological omnivore, having the digestive flexibility and enzymatic capacity to digest and assimilate animal preys ( Camus et al. 2009) and it is also a commercially important species ( Osorio 2002).