(FIG. 12)
Patella terroris Filhol, 1880: 1095; Filhol, 1885: 529. Nacella (Patinigera) illuminata Suter, 1913: 77.
Patinigera terroris – Powell, 1955: 69.
Nacella (Patinigera) terroris – Powell, 1973: 200, pl. 182, figs 3, 4; Powell, 1979: 42, pl. 15, 16.
Nacella terroris – González-Wevar et al., 2017: 862.
Material studied: Perseverance Harbour, Campbell Island (52°33’02.14’’ S, 169°09’08.38’’ E) N = 3.
Shell: The shell shape and sculpture are constant in the three analysed specimens (Fig. 12A–C). The species exhibits a conical morphology, dorsally raised, with a very thick and non-translucent shell (Fig. 12A–F). The anterior part of the animal is laterally compressed (Fig. 12D–F). The shell is of medium size (maximum length 80 mm) and exhibits a high profile. The apex is situated at the anterior 40% of the shell. All the slopes are convex (Fig. 12A– C). The aperture is oval. The surface of the shell is sculptured with raised angular primary radial ribs, weaker secondary ones and concentric growth lines that are visible in the interspaces. The margin of the shell is crenulated. The external coloration is pale reddish-brown and grey. The primary and secondary ribs are red-brown to ash-coloured to dark brown with clearer interspaces. The internal part of the shell has a soft metallic-brown coloration with dark lines corresponding to external colour patterns, bordered by a white/brown halo.
External anatomy: The ventral area of the foot is grey and the epipodial fringe is quite recognizable. The mantle fold is thin and dun-brown coloured. The mantle tentacles are not pigmented and in alternate series of three white and a white longer one (Fig. 12G). The cephalic tentacles are dorsally pigmented with a black line (Fig. 12G).
Radula: The first lateral teeth are set close together on the anterior edge of the basal plates, long and sharp pointed, with two long cusps. The second laterals are broader, wider spaced with three short cusps (Fig. 12H).
Distribution: Campbell Island, sub-Antarctic New Zealand (Fig. 12I).
Habitat: Low intertidal and subtidal rocky ecosystem down to 30 m.
Comments: Multi-locus phylogenetic reconstructions recognized N. terroris from Campbell Island as a distinct taxonomic unit, closely related to Macquarie Island’s N. macquariensis and to N. edgari from Kerguelen and Heard Islands. Phylogenetic relationships and divergence time estimates indicate that Nacella species from New Zealand (N. terroris) and Australia (N. macquariensis) constitute a recent offshoot from the Kerguelen Archipelago (González- Wevar et al., 2017).
MOLECULAR ANALYSES
As previously demonstrated (Nakano & Ozawa, 2004, 2007; González-Wevar et al., 2010, 2017), the monophyly of Nacellidae (Nacella + Cellana), as well as the molecular distinction and the sister relationship between Nacella and Cellana, were highly supported (Fig. 13). Within Nacella, no topological inconsistencies were detected when comparing mitochondrial and nuclear markers. Phylogenetic reconstructions recognized the division of Nacella into two main clades. The first (I) includes South American lineages, while the second (II), those from maritime Antarctica and sub- Antarctic islands (Fig. 13).
In South America, main clade I includes individuals of the new Magellanic lineage (a) N. yaghana sp. nov. (Fig. 13). All the analysed specimens from Pía and Garibaldi Fjords, Beagle Channel, fell within a clearly resolved, reciprocal monophyletic clade and, therefore, represent a new previously unrecognized Nacella species here described (Fig. 13). Lineage (b) includes all the individuals of N. clypeater collected along Central Chile in the Pacific margin of South America between 42°S and 30°S (Fig. 13). Finally, lineage (c) represents the most diverse South American group and includes Magellanic species: N. deaurata, N. flammea, N. magellanica and N. mytilina. As observed in previous studies (González-Wevar et al., 2010), mitochondrial DNA reconstructions recognized the reciprocal monophyly of N. mytilina and N. flammea, but failed to recover that between N. deaurata and N. magellanica. However, 28S rRNA and the concatenated analyses (Fig. 13) recovered the reciprocal monophyly of all four Magellanic species with strong support. Accordingly, the current diversity of Nacella in South America includes three lineages (a–c) and six species (N. clypeater, N. deaurata, N. flammea, N. magellanica, N. mytilina and N. yaghana sp. nov.).
The second main clade II includes Nacella species from sub-Antarctic islands and from maritime Antarctica (Fig. 13). Lineage (d) includes the species N. edgari (Kerguelen and Heard Islands), N. macquariensis (Macquarie Island) and N. terroris (Campbell Island). All the methods and molecular markers recognized N. edgari as a monophyletic unit, including individuals previously labelled N. cf. macquariensis from Heard Island (González-Wevar et al., 2010) (Fig. 13). At the same time, the species N. macquariensis (Macquarie Island) and N. terroris (Campbell Island) are both monophyletic and form a clade closely related to N. edgari (Fig. 13). Lineage (e) includes individuals of N. kerguelenensis (Kerguelen and Heard Islands), but this species was not found at Macquarie Island as reported by Powell (1973). Interestingly, high levels of genetic divergence characterize the sympatric species N. kerguelenensis and N. edgari. In fact, molecular divergence between these sympatric species are similar to those recorded between Antarctic and sub-Antarctic lineages of the genus (González-Wevar et al., 2012b, 2016b). Finally, lineage (f) includes the Antarctic limpet N. concinna and its sister species N. delesserti from the sub-Antarctic Marion and Crozet Islands (Fig. 13). Accordingly, the diversification of Nacella in the Kerguelen Plateau and New Zealand Islands includes two main lineages (d and e) and four species (N. edgari, N. kerguelenensis, N. macquariensis and N. terroris) while maritime Antarctica encompasses a single lineage (f) with two sister species (N. concinna and N. delesserti).