Nacella concinna

NACELLA CONCINNA (STREBEL, 1908)

(FIG. 8)

Patella polaris Hombron & Jacquinot, 1841: 191 (not of Röding, 1798); Martens & Pfeffer, 1886: 101, pl. 2, figs 11–13; Melvill & Standen, 1907: 124.

Nacella polaris – Pilsbry, 1891: 120, pl. 49, figs 21–27; Lamy, 1906: 10, Lamy, 1911: 26.

Nacella aenea var. polaris – Pelseneer, 1903: 14.

Patinella polaris – Strebel, 1908: 81, pl. 5, figs 79–82.

Patinella polaris var. concinna Strebel, 1908: 81, pl. 5, fig. 77.

Lepeta depressa Hedley, 1916: 42, pl. 6, fig. 64; Arnaud, 1972: 114; Dell, 1972: 32, figs 19, 24–25; Egorova, 1982: 14, fig. 75.

Nacella (Patinigera) polaris – David, 1934: 127; Zelaya, 2005: 111, fig. 2.

Patinigera polaris – Powell, 1951: 82; Walker, 1972: 49; Castellanos & Landoni, 1988: 25, pl. 4, fig. 8.

Patinigera polaris concinna – Powell, 1951: 83; Castellanos & Landoni, 1988: 26, pl. 4, fig. 5.

Nacella (Patinigera) concinna – Powell, 1973: 193–195, pl. 175, figs 1–5; Picken, 1980: 71; Ramírez 1981: 58; 71; Picken & Allan, 1983: 273; Brêthes et al., 1984: 161; González-Wevar et al., 2010: 116; González-Wevar et al., 2011b: 220.

Patinigera polaris polaris – Castellanos & Landoni, 1988; 26, pl. 4, fig. 8.

Nacella concinna – Beaumont & Wei, 1991: 443; Linse et al., 2006: 997; de Aranzamendi et al., 2008: 875; Hoffman et al., 2010a: 287; 2010b: 765; 2011: 55; 2012a: 922; 2012b: 1; 2013: 1; González-Wevar et al., 2013: 5221; 2017: 863; Rosenfeld et al. 2017: 3.

Nacella cf. concinna – Hain & Melles, 1994: 36, fig. 4.1. Nacella polaris concinna – Aldea, Olabarria & Troncoso, 2008: 355; Aldea & Troncoso, 2009; 49, fig. 2. Nacella polaris polaris – Aldea et al., 2008: 49, fig. 3.

Material studied: Rothera Station, Adelaide Island, Antarctic Peninsula (67°34’03.17’’ S, 68°07’17.40’’ W) N = 50; South Bay, Anvers Island (64°53’21.55’’ S, 63°35’43.44’’ W) N = 40; Yelcho Station, Doumer Island, Palmer Archipelago, Antarctic Peninsula (64°53’34.29’’ S, 63°35’09.04’’ W) N = 40; Covadonga Bay, Antarctic Peninsula (63°19’13.96’’ S, 57°53’54.15’’ W) N = 50, James Ross Island, East Antarctic Peninsula (63°55’14.33’’ S, 57°15’54.22’’ W) N = 40, Hannah Point, Livingstone Island, South Shetland Islands (62°39’11.31’’ S, 60°36’55.44’’ W) N = 40; Fildes Bay, King George Island, South Shetland Islands (62°12’28.68’’ S, 58°57’24.89’’ W) N = 80, Admiralty Bay, King George Island, South Shetland Islands (62°05’14.40’’ S, 58°27’29.57’’ W) N = 80; Deception Island (62°55’14.52’’ S, 60°35’14.62’’ W) N = 50; Elephant Island (61°05’12.24’’ S, 55°20’22.54’’ W) N = 29; South Orkney Island (60°44’20.03’’ S, 44°44’17.05’’ W) N = 26; Signy Island, South Orkneys Islands (60°43’22.22’’ S, 45°35’16.14’’ W) N = 30; South Georgia (54°17’00.11’’ S, 36°29’13.04’’ W) N = 100.

Shell: The shell shape and sculpture are very variable (Beaumont & Wei, 1991; de Aranzamendi et al., 2008; Hoffman et al., 2010b; González-Wevar et al., 2011b) (Fig. 8A–C). The species exhibits a conical morphology, dorsally raised, with a thick and non-translucent shell (Fig. 8A–F). The anterior part of the animal is laterally compressed (Fig. 8D–F). It has a large shell (maximum length 120 mm) and a variable profile (Fig. 8A–C). The apex is situated at the anterior 30–40% of the shell’s length (Fig. 8A–C). All the slopes of the shell are convex (Fig. 8D–F). The aperture of the shell is oval. The surface of the shell is sculptured with weak primary radial ribs, weaker secondary ones and concentric growth lines. The margin of the shell is highly crenulated. The external coloration is very variable (pale brownish/green/grey to dark brown and black). The internal part of the shell varies from creamy nacreous to dark bronzy-brown with dark lines corresponding to external colour patterns.

External anatomy: The ventral area of the foot is black and the epipodial fringe is highly recognizable. The mantle fold is thick and dun-brown coloured. The mantle tentacles are in alternate series of a single black longer tentacle and three shorter ones (white/black/white) (Fig. 8G). The cephalic tentacles are dorsally pigmented with a black line (Fig. 8G).

Radula: The first lateral teeth are set close together on the anterior edge of the basal plates, of medium length and with two spoon-like cusps. The second laterals are broader, wider spaced, with two spoonlike cusps. One of them is very small and the other is bigger and broader (Fig. 8H).

Distribution: Maritime Antarctica, including ice-free rocky ecosystems of the Antarctic Peninsula, the South Shetland Islands, South Georgia, South Orkneys, Bouvet, Elephant Island, Seymour Island, Paulet Island, Wander Island, Anvers Island and Peterman Island (Fig. 8I).

Habitat: Intertidal and subtidal between 0 and 150 m depths.

Comments: The Antarctic limpet represents a single genetic population along maritime Antarctica (González-Wevar et al., 2011b, 2013, 2016b, 2017), but thispopulationdifferesmarkedlyfromthosefromSouth Georgia (González-Wevar et al., 2013). The inter- and subtidal morphotypes were once regarded as separate subspecies, N. polaris polaris and N. polaris concinna (Powell, 1951). Nevertheless, genetic comparisons using allozymes (Beaumont & Wei, 1991), mtDNA (González-Wevar et al., 2011b, 2013, 2016b) and AFLPs (Hoffman et al., 2010b) confirmed that these forms represent a single evolutionary unit. Accordingly, shell height, shape and sculpture differences in the Antarctic limpet represent phenotypic plasticity in the species.