Plumatella mukaii Wood, 2001

(Figure 2 D)

Plumatella mukaii Wood, 2001: 51, figs 1, 3–6.

Plumatella princeps emarginata: Kraepelin 1887: 119, pl. 4(108), pl. 5(123). Plumatella emarginata: Toriumi 1952b: 320 (part); Mukai 1999: 51, figs 2A, 3C, 5A, 7A (part); Mukai & Kobayashi 1988: 205 (part); Mukai et al. 1990: 51 (part).

Material examined. Several floatoblasts from Benoki Dam, village of Kunigami.

Description. Colony tubular, branched, well chitinized (Wood, 2001). Floatoblasts elliptical in our specimen, shorter than those of P. emarginata; 307–408 (360±32) μm long by 195–237 (214±13) μm wide (n=10), with length/width ratio of about 1.6. Ventral fenestra almost circular. Surface of both valves entirely covered with villi (Fig. 2 D). Dorsal fenestra small, less than half the length of the ventral fenestra. Annulus of floatoblast sculptured with very coarse pavement and covered with minute villi. Floatoblast valves asymmetrical in lateral view, the ventral valve markedly convex, the dorsal valve almost flat.

Distribution. Reported from eastern Asia and Thailand (Wood et al. 2006); collected from many localities in Japan; ranging from Okinawa to Aomori Prefecture, northern Honshu Island.

Remarks. Plumatella mukaii was originally reported as P. emarginata (Toriumi 1952b; Mukai 1999; Mukai & Kobayashi 1988; Mukai et al. 1990). Wood (2001) discovered that the floatoblast of Japanese P. emarginata is much shorter than that of P. emarginata from North America and Europe and has minute villi on the surface, and described the Japanese material as a new species, P. m u k a i i.