Abstract
The patellogastropod limpet genus Nipponacmea is widely distributed in Japan and adjacent East Asia. Species identification within Nipponacmea is challenging due to the high variation in shell morphology. In this study, we examined the taxonomy of this genus represented by nine nominal species from 43 localities (including type localities). Results of the molecular phylogenetic analysis revealed that: (1) N.gloriosa, the sole species in this genus inhabiting the subtidal zone, represents the most basal independent branch; (2) the remaining species are divided into two large clades with lower- and higher-apex shell profiles; and (3) the high-apex morphology was derived from the low-apex type. The terminal clades defined using the molecular data were consistent with nine morphospecies and had 100% bootstrap values, strongly supporting the conventional taxonomy of Nipponacmea. Although morphological similarities do not always reflect phylogeny, the set of morphological characters used in the current taxonomy were proven to be adequate for diagnosis. In conclusion, this study provided solid evidence to uphold the monophyly of known species of Nipponacmea in Japan and demonstrated the usefulness of morphological characters for species diagnosis.
Highlights
Limpets belonging to the clade Patellogastropoda are abundant in the intertidal rocky shores globally and are important in marine biology (Branch 1985a, b)
A total of 130 Nipponacmea individuals morphologically identified as N. schrenckii (12), N. fuscoviridis (29), N. concinna (15), N. radula (8), N. boninensis (3), N. habei (9), N. teramachii (16), N. nigrans (27), and N. gloriosa (11) were sequenced (Table 2)
The monophyly of Japanese Nipponacmea species has not been previously tested using molecular characters; it was strongly supported by the data obtained from the present study (Fig. 2)
Summary
Limpets belonging to the clade Patellogastropoda are abundant in the intertidal rocky shores globally and are important in marine biology (Branch 1985a, b). Molecular phylogenetic analysis and comparison of morphological characters have previously been performed for limpets with ambiguous taxonomies (Lottia: Simison and Lindberg 2003; Notoacmea: Nakano and Spencer 2007; Nakano et al 2009a; Patella: Mauro et al 2003; Patelloida: Nakano and Ozawa 2005; Nacella: de Aranzamendi et al 2009; González-Wevar et al 2011; Cellana: Reisser et al 2011 and 2012). There is no fixed threshold for species delimitation using genetic distances, and species taxonomy must be based on the level of continuity of the morphological characters
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