Morphological and genetic differentiations of the stalked barnacle Heteralepas japonica Aurivillius, 1892, with description of a new species of Heteralepas Pilsbry, 1907, from the Philippines

Species of Heteralepas are called "naked barnacles" because they have no external shell plates or valves on the capitulum. Taxonomy in Heteralepas is often confusing due to the lack of calcareous hard characters for comparison and the high degree of intra-specifi c morphological variations in the stalk, shape of capitulum and the cirral segments of the barnacles. In the present study, barnacles initially identifi ed as Heteralepas japonica collected in Philippine, Japanese and Taiwanese waters exhibit diagnostic morphological and genetic differentiation. Heteralepas japonica from the Philippines had one to three crests on the carinal margin, whilst the Japan and Taiwan population had at most one crest on the carinal region. The wall of the capitulum of the Japanese and Taiwanese population is thicker than the Philippine populations. Phylogenetic analysis of COI and 12S sequences from individuals initially identifi ed as H. japonica resulted in two distinct clades with high nodal support ( 85\% for all analyses). The fi rst clade consisted of all H. japonica from the Philippines, while the three H. japonica individuals from Taiwan and the single individual from Japan form the second clade. The sequence divergences among the Philippine and Taiwanese clades were ˊ 14\% and ˊ 8.5\% for uncorrected p-distance in the COI and 12S regions, respectively. These values were much greater than sequence divergences within each clade (≤ 2.1\%). Results suggest that Heteralepas from the Philippines and Taiwan are two different species. Type locality of H. japonica is at Hirado Strait, West Kyushu, Japan and the morphological features of the Japan and Taiwan populations matched with the previous descriptions of H. japonica collected from Japanese waters. We, therefore, recognise the Philippine form as a new species, described herein.