Two specimens of a remarkable new neoverrucid and a few metamorphosing cyprid larvae containing its inferred first juvenile stage were found among the barnacles collected by the submersible Nautile during the BIOLAU Expedition (1989) to the Lau Back-Arc Basin, Tonga. The new form, Imbricaverruca yamaguchii n. gen. and n. sp., differs from the only previously known species, Neoverruca brachylepadoformis Newman, 1989, in having an operculum with a relatively large, permanent median latus and a reduced primary wall supported by relatively large, close-fitting, imbricating plates, the lowermost of which are apparently not deciduous. On the other hand, it has a superficial facies similarity with verrucids. However, its construction and inferred first juvenile stage are quite different whereby it appears to represent a relatively specialized neoverrucid rather than an evolutionary step leading to proverrucids and/or verrucids. The new form not only provides evidence that a significant diversification took place within the neoverrucids, it constitutes a significant addition to our knowledge of the vent-inhabiting cirriped fauna of the Lau Basin already considered the most diverse known in the world.
Vent fauna, thoracican first juveniles, systematics, evolution, biogeography.