Chthamalus williamsi sp. nov.

Figures 2–5

Material examined. Holotype. NMNS-006534-00001. Intertidal rocks (low shores, at the same tidal zone as Megabalanus volcano) at Shi-Ti-Ping, Hualien, Taiwan (23°29.30’N, 121°30.30’E, 12 May 2009). Paratype. NMNS-006534-00002. Cheng Gong, Taitung, Taiwan (23°05.46’N, 121°22.33’E, 0 2 Sep. 2008). Paratype. ASIZCR-000328. Cheng Gong, Taitung, Taiwan (23°05.46’N, 121°22.33’E, 0 2 Sep. 2008).

Diagnosis. Shell conical; 6 plates, external surfaces white, smooth or with faint ribs; scutum equilateral triangular, tergal articular margin straight, external surface of scutum with horizontal striations; tergum triangular, scutal articular margin straight, spur blunt.

Description. Shell small, about 3.0 mm basal diameter, conical; 6 plates (rostrum, carina, paired lateral and paired rostral-lateral; Fig. 2 A–D), externally white, surface smooth or with faint ribs, inner operculum pale orangecoloured; carina and rostrum with a pair of alae, carina short and wide, alae large; rostrum long and narrow, alae large; rostral-lateral triangular, interior surface with central mid rib, radii wide; lateral base wide, alae and radii present (Fig. 2 D); scutum white, triangular, tergal articular margin straight, perpendicular to basal margin, articular ridge not prominent, long with length extending 2/3 length of tergal articular margin, articular furrow narrow, deep, occludent margin inclined with fine teeth, scutal adductor scar oval, obvious, external surface of scutum with horizontal striations (Fig. 2 E, F); tergum white, triangular, scutal articular margin straight, extending down to spur, spur blunt, wide, about ½ width of basal margin, articular furrow wide, shallow, basal margin slightly concave (Fig. 2 E, F), 5 fine depressor crests at basal margin, external surface striated.

Cirrus I without conical spines on dorsal surface, posterior ramus 5-segmented, anterior ramus 6-segmented (Fig. 3 A), both rami with serrulate setae, setae without basal guard (Fig. 4 A–C); cirrus II, anterior ramus 5- segmented, posterior ramus 7-segmented (Fig. 3 B), both rami with 2 types of serrulate setae, bidentate and plumose setae, all setae without basal guard (Figs 4 D–F, 5K, L); cirrus III with rami equal length, anterior ramus 14-segmented, posterior ramus 12-segmented (Figs 3 C, 4G), intermediate segments of cirrus III composed of 5 pairs of long serrulate setae (Fig. 4 H, I); cirrus IV with anterior ramus 14-segmented, posterior ramus 15- segmented (Fig. 3 D); cirrus V with anterior ramus 18-segmented, posterior ramus 15-segmented (Fig. 3 E), intermediate segments of both rami with 3 pairs of long serrulate setae and 2 pairs of shorter setae (Fig. 4 J); cirrus VI with anterior ramus 19-segmented, posterior ramus 17-segmented, intermediate segments of anterior and posterior rami composed of 3 pairs of long serrulate setae and 2 pairs of shorter setae (Fig. 4 K); penis long, slender, sparse setae along length, tip with dense bundle of setae (Fig. 5 I, J).

Maxilla bilobed, serrulate setae on both lobes (Fig. 5 A, B); maxillule notched, 3 large setae above notch, 16 setae below notch (Fig. 5 C, D); mandible with 4 teeth, fourth bidentate, lower margin straight, with 14 setae, inferior angle with pair of large setae (Fig. 5 E, F); labrum concave, notch absent, dense setae at mid region of cutting margin, latter with numerous fine teeth (Fig. 5 G, H).

Etymology. Chthamalus williamsi is named in honour of Prof. Gray A. Williams, Director of the Swire Institute of Marine Sciences, School of Biological Science, the University of Hong Kong, for life-long friendship and mentorship with the first author and for his contributions to the intertidal ecology in the South China Sea.

Distribution. Chthamalus williamsi sp. nov. is common inside crevices of the mid shore of the intertidal zone, and on the shell surfaces of the barnacle Megabalanus volcano (Pilsbry, 1916) and M. tintinnabulum (Linnaeus, 1758) on low shores of the eastern waters of Taiwan. Chthamalus williamsi has not been identified previously from Taiwan as it is not easily spotted, due to its small size and low shore location. This species is absent from the N and NE coasts of Taiwan although intensive sampling was conducted (Fig. 1), suggesting its distribution may be associated with the Kuroshio Current.

Molecular analysis. From both maximum likelihood and Bayesian inference trees of a COI region, Chthamalus williamsi shows a distinct divergence from C. challengeri, C. dalli, C. moro, C. malayensis and C. sinensis (sequence divergence>0.13 K2P distance from all the Chthamalus species compared; Table 1). Chthamalus sinensis and C. neglectus grouped in the same clade, suggesting C. neglectus is a synonym of C. sinensis (see Liu & Ren 2007 for synonyms of C. neglectus and C. sinensis).