Morphological and genetic differentiation of the acorn barnacle Tetraclita squamosa (Crustacea, Cirripedia) in East Asia and description of a new species of Tetraclita

The common intertidal barnacle Tetraclita squamosa occurs in two morphologically and genetically distinct forms in East Asia. The north-western Pacific form (Japan, Okinawa and Taiwan) has green parietes and the tergo-scutal flaps are black without any patterns. The south China form (Xiamen, Hong Kong) also has green parietes but the tergo-scutal flaps are black with two white spots on the tergal and scutal margin. Compared to the NW Pacific form, the south China form has a beaked tergum, a sharper tergal spur and cirrus I lacks serrulate type setae that have four rows of setules. The two forms differ by 15–16% in COI divergence, which is comparable to values for other congeneric barnacle species. The 12S rRNA and ITS1 sequences are also distinct between the two forms. Our results support the conclusion that the two forms are genetically differentiated species. We describe the NW Pacific form as a new species, Tetraclita pacifica . We are treating the other species as Tetraclita squamosa based on the fact that Pilsbry, in 1916, redescribed T. squamosa squamosa using samples collected from south China and the Philippines. Further studies are needed to confirm the identity and geographical distribution of the 'widely distributed' T. squamosa in the Indo-West Pacific.