Calloplax vivipara (Plate, 1899)

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

Calloplax vivipara (Plate, 1899) Plate 1, Fig. 3; Table 2

Callistochiton viviparus Plate, 1899: 154, pl. 9, figs 267-281; Dall 1909: 246; Gigoux 1934: 281; Boudet 1945: 134; Leloup 1956: 46; Stuardo 1959: 144: Smith 1966: 436, 437, 441, 442. Chiton janeirensis , Var.?: Gray 1828: 5; Sowerby 1840: 6, sp. no. 78 (spelled janierensis). Calloplax viviparus : Ferreira 1978: 60, figs 2 & 5.

Description.

Animal of small size, up to 12 mm in examined specimens, elongate oval, moderately elevated, color of tegmentum tan or creamy white. Head valve semicircular, sculpture with about nine equally spaced, nodulose, annulate and well defined radial ribs. Intermediate valves rectangular, lateral areas well defined, sculptured with two strong radial ribs. Central area with about eight longitudinal riblets per side, well-marked in the pleural areas but becoming obsolete at the jugum. The riblets tend to converge anteriorly and are not latticed. Posterior valve semi-oval, elevated at the central mucro, with nine well defined radial ribs. Girdle yellowish white, dorsally covered with small scales (After Ferreira 1978).

Material examined.

Specimens found under rocks in a tidal pool at Obispito (MPCCL 3072014B, 1 specimen), Sur de Playa Ramada and under rock slabs sunken under boulders in Peninsula Calderilla (SBMNH 452241, 1 specimen).

Distribution.

Plate (1899) described this species for Isla Pacharos (= Pájaros), near Coquimbo, Chile (29°58'S; 71°21'W). Ferreira (1978) additionally recorded this species from the intertidal of Pozo Toyo, South of Iquique, Tarapacá Province (20°25'S; 70°10.5'W) and mainland East of Isla Santa María, North of Antofagasta, Antofagasta Province (23°25'S; 70°36'W) from specimens housed at the LACM. A specimen labelled Chiton janeirensis (NHMUK 197742) identified by Ferreira (1978) as Calloplax viviparus extended the southern distribution of this species at Valparaiso (33°02'S; 71°38'W). This is the first time this species is recorded, in the field, since its description and the present record fills a gap in the distribution in Chile of this rare species.

Remarks.

This is a rare species, found in only two of the locations under study; in both places this species was found under rocks sunken in tidal pools, associated to encrusting sponges and to communities of the small mussel Brachidontes granulata (Hanley, 1843). According to Plate (1899) this species is ovoviviparous; that cited author found about 15 embryos, some with seven shell valves, in the ovary of a single specimen. In fact, this is the only chiton species ever reported to be ovoviviparous ( Pearse 1979). This species is somewhat similar to Callistochiton pulchellus (Gray, 1828), differing in the coarse sculpture (especially in the anterior valve, with fewer and stronger ribs), the presence of longitudinal riblets in the central areas, and the more yellowish body color.