Nacella clypeater

NACELLA CLYPEATER (LESSON, 1831)

(FIG. 3)

Patella clypeater Lesson, 1831: 419; Reeve, 1854: pl. 16, figs A, B; Huppé, 1854: 259.

Nacella (Patinella) clypeater – Pilsbry, 1891: 122.

Patinigera clypeata – Dell, 1964: 273.

Nacella (Patinigera) clypeater – Powell, 1973: 193, pl. 175, figs 1, 2; Ramírez, 1981: 52; Valdovinos & Ruth, 2005: 504.

Nacella clypeater – Aldea & Valdovinos, 2005: 369; González-Wevar et al., 2010: 116; 2017: 863.

Material studied: Coquimbo (29°58’04.68’’ S, 71°22’00.79’’W) N = 40; Valparaíso (33°00’56.98’’S, 71°33’39.62’’W) N = 25; Pichilemu (34°25’29.96’’S, 72°02’39.31’’W) N = 20; Tubul (37°13’11.09’’S, 73°26’35.55’’W) N = 35; Mehuín (39°26’39.04’’S, 73°13’52.63’’W) N = 25; La Misión (39°47’44.48’’S, 73°23’59.17’’W) N = 40; Pucatrihue (40°32’39.92’’S, 73°43’16.68’’W) N = 25.

Shell: The shell shape and sculpture are relatively constant in the analysed individuals from different localities along the Chilean Central coast (Fig. 3A–F). The species exhibits a conical morphology, dorsally depressed with a relatively thick and non-translucent shell (Fig. 3A–C). The anterior part of the animal is laterally compressed (Fig. 3D–F). The shell is large (maximum length 120 mm) with a low profile. The apex is situated at the anterior 30% of the shell. The anterior slope of the shell is slightly concave, while the lateral and the posterior slopes are convex (Fig. 3A–C). The aperture of the shell is circular. The surface of the shell is sculptured with fine, rounded near-radial ribs and concentric growth lines beginning below the apex. The margin of the shell is relatively even. The external coloration varies (grey, green and brown) with clear white, yellow and creamy ribs. The internal part of the shell exhibits silvery to pale bronze, with a brown spot that corresponds to the impression of the body.

External anatomy: The ventral area of the foot and the mantle fold are creamy white coloured and the epipodial fringe is recognizable. The mantle fold is thin and bordered by a black narrow line. Mantle tentacles are in alternate series of three short ones and a slightly longer one and lack pigmentation (Fig. 3G). The cephalic tentacles are not pigmented (Fig. 3G).

Radula: See Valdovinos & Rüth (2005) (Fig. 3H).

Distribution: Pacific margin of the Chilean coast between 42°S and 30°S (Fig. 3I).

Habitat: Low intertidal and subtidal rocky shores between 0 to 20 m depths.

Comments: Field observation along the Chilean coast shows that N. clypeater exhibits a patchy distribution being highly abundant in some localities and completely absent at others. In fact, Aguilera (2011), in a rocky intertidal trophic study across the Chilean coast, did not record the presence of N. clypeater and, therefore, considered it as an uncommon inter- subtidal species. Population-based analyses in the species suggest that N. clypeater represents a single genetic unit across its distribution and exhibits extremely low levels of mtDNA (COI) genetic diversity across its distribution (unpublished data).