Plumatella emarginata

Description. Observed colonies tubular, branching, shiny dark brown or well encrusted. Tentacle number 20 to 50. Floatoblasts in Okinawan populations elliptical, elongate, 329 – 527 (427 ± 67) μm long by 211 – 248 (226 ± 11) μm wide (n = 10), with length / width ratio of about 1.9 (Fig. 2 C); fenestra of ventral valve almost circular, more than four times diameter of fenestra of dorsal valve; both ventral and dorsal fenestrae covered with tubercles; annuli textured with coarse pavement; floatoblast valves asymmetrical in lateral view, the ventral valve convex, the dorsal almost flat. Sessoblasts with tuberculate surface and smooth annulus, 437 – 466 (451 ± 12) μm long by 273 – 301 (282 ± 13) μm wide (n = 4).

Remarks. Floatoblasts of P. emarginata from Okinawa are larger than in other regions (average length 427 μm; SD 67.0) and sometimes have strongly elevated tubercles. Colonies and floatoblasts appear to be variable in form, and the nominal species may include several synonymous species. Although we did not observe sessoblasts of this species from Okinawa, we identified our material as P. emarginata on the basis of the floatoblast and colony morphology.

Distribution. Broadly distributed worldwide; distributed in Japan from Okinawa to Hokkaido.

Material examined. Floatoblast from pond in city of Uruma; floatoblasts from Ryutan-ike pond next to the castle, city of Naha; floatoblasts and colony with floatoblasts and sessoblasts from Fukuji Dam, village of Higashi; floatoblasts and colony with floatoblasts and sessoblasts from Benoki Dam, village of Kunigami.