Hexechamaesipho pilsbryi (Hiro, 1936) is a high shore barnacle discovered by F. Hiro in Honshu, Japan in 1936. In the northwest Pacific, H. pilsbryi was found from Honshu to Taiwan but not along the mainland coast of China, suggesting it is an insular species and the biogeography
is influenced by the Kuroshio Current. Hexechamaesipho pilsbryi had not been previously reported in Taiwan, so there may have been a distribution extension. Mean abundance (> 80% cover) and cohort numbers (> 3) of H. pilsbryi were higher in Okinawa than in Honshu and Taiwan
(< 50% cover, < 3 cohorts), suggesting that the Honshu and Taiwan populations may be derived from the Okinawa population. The decreased adult density in Honshu and Taiwan may be due to a reduced larval supply, harsher environment outside Okinawa waters, or the result of competition/predation
interactions. Both H. pilsbryi and Nesochthamalus intertextus (Darwin, 1854) appear to be adapted to a subtropical climate zone, bridging the “Japan region” and the “Indo-Polynesian province” proposed by Briggs (1974). The shape of the tergum and mandibles
of H. pilsbryi is variable. From SEM studies, the setae on the cirri and mouth parts have a consistently similar form throughout the presently known geographical range of H. pilsbryi. Cirrus II invariably carries multicuspidate setae (= card setae or grapples), supporting the
repositioning of this species from the sub-family Chthamalinae to the sub-family Notochthamalinae by Poltarukha (1996).
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