How do whale barnacles live on their hosts? Functional morphology and mating-group sizes of Coronula diadema (Linnaeus, 1767) and Conchoderma auritum (Linnaeus, 1767) (Cirripedia: Thoracicalcarea)

Whale-associated barnacles are intriguing in terms of their planktonic food sources, mating habits, and mechanisms of host attachment. We present observations of the whale-associated barnacles Coronula diadema (Linnaeus, 1767) and Conchoderma auritum (Linnaeus, 1767) obtained from dead humpback whales (Megaptera novaeangliae (Borowski, 1781)) collected in Korea. Shell bases of Coronula diadema are inflected and sharp-edged with hollow coring tubes at the periphery. The coring tubes are filled with whale skin, supporting the model that shell accretion into the whale skin is achieved by basal constriction to achieve strong attachment. Conchoderma auritum attaches to the shell surfaces of Coronula and has a pair of tubular ear-shaped structures on the capitulum. Both species have short and thick-segmented cirri that allow feeding in strong currents. The distal ends of the cirri in both species are often equipped with sharp, large claw-like setae, which are likely used to capture large zooplankton for food. Coronula diadema and Conchoderma auritum are simultaneous hermaphrodites. Coronula diadema can mate up to nine surrounding individuals. Conchoderma auritum lives in clumps and mating group size can up to 26 individuals.