Capitulum with two reduced or rudimentary valves widely separated from each other. A thick membrane and two ear-like tubes behind terga; these 'ears' communicating with mantle cavity in adults; in older specimens folded, sometimes as long as capitulum. Valves in young specimens well developed, but small or even absent in adults. Scutum small, bilobed, weakly calcified and of variable shape; umbo in middle of valve. Tergum small, linear or absent in fully-grown specimens. Carina rudimentary or absent. Peduncle without scales, cylindrical, distinctly marked off from capitulum.
Mouth parts: Labrum with fine teeth on inner margin. Palpus conical with setae along all the inner side. Mandible a little variable, as a rule with four or five teeth, finely pectinate on lower margin, inferior corner narrow. Maxilla I with two upper spines (one small) and some small se tee below these. Front margin with spines and with three or four steps, as typical of the family. Maxilla II simply arched with long setae round margin.
Cirri: Much flattened with protuberant segments, especially in cirri I and II. Filamentary appendages well developed, seven on each side, none at base of cirrus Vl. Filaments at the base of the longer cirri nearly twice as long as the cirri themselves. No caudal appendages.
Hermaphrodite. Penis short and stout as in other whale barnacles.
Length of peduncle two or tree times as long as capitulum, which is generally about 35 mm, but can be up to 70 mm long.
Variable; sometimes, especially in young specimens, five distinct longitudinal bands of dark purple on peduncle, tending to become confluent on capitulum; in other cases capitulum spotted or nearly uniformly purple; specimens situated on black objects, for instance the tail of a whale, almost black.
Pelagic. Attached to the Whale barnacle Coronula diadema and sometimes Coronula reginae. It seems to be a rule that no Coronula is without a Conchoderma. Whether this is a form of symbiosis has been discussed by Broch (1924b). Specimens from northern waters have been taken from humpback whales (Megaptera novaeangliae ) or from teeth of bottle-nosed whales (Hyperodon spp.). In the Antarctic C. auritum has also been found on baleen plates of whales and on their tails. In tropical and subtropical parts of the oceans it can also be found attached to ships' hulls and other floating objects, to slow moving fishes or to the tail of a large eel, but never on soft objects. It seems as small odontocetes are only rarely infected with C. auritum (Van Bree, 1971).
Distribution in the North Sea:
N coast of Norway south to Lofoten, Jan Mayen, Iceland, Faeroes-Iceland area, Shetlands, Belgium, Skagerrak, and Denmark (recorded on a ship). The finds are sporadic, though the distribution in the area is certainly wide. Recorded from W but not E Greenland, probably due to the scantiness of the investigations.