Complemental males are described for the first time in this deepwater family of balanomorph barnacles. The males are usually lodged externally on the tergum, in the angle formed between the articular margin and the articular ridge. Sometimes they occur in the apex angle of the carina. Compared with similar-sized individuals attached to the outside of the parietal shell plates, the body of the male is dominated by testes and seminal vesicles, the latter packed with sperm, and the penis is 4 to 5 times longer. The sexual condition is compared with that in other barnacles, and the mode of sex determination is discussed.