Abstract
A new mangrove barnacle, Balanus thailandicus sp. nov., is described from the Puyu Canal, Tamalung Bay, Satun, southwest Thailand. The new species has the common characteristics of the Balanus amphitrite complex and is more or less sympatric with B. reticulatus, B. amphitrite, B. patelliformis, and B. variegatus. Balanus thailandicus is most similar to B. reticulatus, but it is clearly distinguishable from the last three mentioned species of the complex in having the parietes folded or ribbed in adults but smooth in juveniles, parietal tubes solid in the upper half and interrupted by transverse septa in the lower part, the large number of articles in the anterior ramus of cirrus I, and erect hooks below the posterodistal angles of the articles of cirri III and IV.
