We examined the diel settlement fluctuations of the subtidal barnacles Megabalanus rosa and Balanus trigonus during summer at Sakihama in Okkirai Bay, Iwate Prefecture, Japan. PVC plates were suspended vertically close to a pier wall just below low tide level and inspected every six hours. The number of settled barnacles of both species were counted together. Greater settlement occurred on the illuminated sides of the panels than on the shaded sides. The settlement rate during the 04:00-10:00 interval was highest, that in the 10:00-16:00 interval followed, and those in the 16:00-22:00 and 22:00-04:00 intervals were the lowest. On clear days, the settlement rate during the 04:00-10:00 interval was significantly higher (p<0.01) than during the 10:00-16:00 interval, but the settlement rates on cloudy or rainy days were not significantly different between the two intervals. These results indicate that a great change in illumination is more of a settlement stimulus for dark-adapted larvae than for light-adapted larvae. Effects of other environmental factors on diel and day-to-day fluctuations in settlement are discussed.

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The distribution of living and fossil coral-inhabiting barnacles (family Pyrgomatidae) was investigated in Japan. Twenty eight species of living coral barnacles were found from southwest Japan, but 2 species, Cantellius acutus and C. sumbawae, which were reported by UTINOMI (1962) and OGAWA and MATSUZAKI (1990) respectively, were not among them. Seven species are new records for Japan: Cantellius arcuatus, C. sinensis, C. tredecimus, C. sp. aff. albus, C. sp. aff. maldiviensis, Creusia spinulosa, and Savignium sp. aff. orientale. The number of species of living corals decreases markedly from the Okinawa region towards the north; however, the number of species of coral barnacles does not decrease as quickly. Eight species of fossil coral barnacles were found in the Holocene Numa Formation of the Boso Peninsula, central Japan. The species composition of living corals in the south Kii Peninsula, west Japan, resembles that of the fossil corals in the Numa Formation; however, the species composition of living coral barnacles in the south Kii Peninsula is distinctly different from that of the fossil coral barnacles in the Numa Formation.

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