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English: Thoracica. A, nauplius larva of Balanus improvisus. Note the presence of frontal horns. B, cypris larva of Amphibalanus amphitrite, showing the pair of extended first antennules and six pairs of thoracopods. C, Anelasma squalicola, a parasite of deep-sea lantern sharks (Etmopterus). The cirri are rudimentary, and the base of the peduncle has a root-like structure embedded inside the tissue of the shark to absorb nutrients. D, Fistulobalanus albicostatus, common on mangrove tree trunks. E, the family Pyrgomatidae are associated with scleratinian corals, and the bases are embedded in the coral skeleton. Cantellius sp. extending the cirri. F, Ibla cumingi, which is located at the most basal position on the molecular phylogenetic tree of thoracican barnacles. G, Megabalanus, Amphibalanus and Lepas inhabiting the capitulum of a penduculated barnacle. H, Capitulum mitella, a stalked barnacle inhabiting rocky shores. In molecular phylogenetic analyses, it is the sister to Anelasma (see C). I, Conchoderma, a stalked barnacle with reduced shell plates, epibiotic on many marine taxa, mostly crabs and whales. J, An early dwarf male settled on the surface of an adult Heteralepas. K, Octolasmis cor lives exclusively on the surface of crab gills. L, Scalpellum scalpellum, a stalked barnacle epibiotic with hydroids. The inserts in LM (upper) and SEM (lower) shows the hermaphrodite receptacles, which can house dwarf males. Inserts show a dwarf male with extended penis (upper) and an SEM micrograph of the receptacle structure. M, Waikalasma is a deep-sea inhabitant, having a row of imbricating plates on the base of shells. N, Chthamalus malayensis is common on intertidal shores. O, Tetraclita, with four shell plates, common on rocky and tropical shores.