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Abstract The discovery of bivalved sea slugs in the family Juliidae revolutionized our understanding of shell evolution in molluscs. However, relationships among lineages remain unclear, with generic names shared by extant and fossil taxa. Juliidae provide important fossil calibration points for dating phylogenies and for understanding the convergent evolution of a bivalved shell. Here, we present a revision of the systematics and classification of members of the Juliidae including Recent and fossil taxa by integrating molecular data from five genes, geometric morphometrics, and anatomical data. A list of all juliid taxa previously described is provided, along with diagnoses and remarks on genus-level names. Results from a geometric morphometric analysis support a new classification scheme, in which the genus Berthelinia, previously used for Recent and fossil taxa, is restricted to fossil species, and the genera Julia and Edenttellina are used exclusively for Recent species. Species of Edenttellina supported by molecular analyses are illustrated and anatomical details provided, including examination of protoconchs, radular teeth, and reproductive structures by scanning electron microscopy, along with illustrations of existing type material. Distinct biogeographical patterns in Julia and Edenttellina are discussed in the context of ecological differences between these two taxa, including host specificity and developmental mode. 

Abstract The genus Cyerce Bergh, 1870 has been a model for the study of defensive strategies, including chemical defences, ceratal autotomy, and crypsis or aposematism. Specialization on different algae and diverse genital armatures also make Cyerce a useful system for investigating speciation by host shift versus sexual selection. Here, we review the genus Cyerce in the Pacific and Indian oceans using molecular and morphological data. Two mitochondrial genes (COI and 16S) and one nuclear gene (H3) were sequenced from 154 specimens, including representatives from the Atlantic Ocean. Bayesian and maximum likelihood analyses were used to generate phylogenetic hypotheses. Species delimitation analyses performed on COI sequences recovered 17 genetically distinct Pacific and Indian Ocean species of Cyerce, 10 of which are new to science. Nine new species are named herein (C. takanoi sp. nov., C. katiae sp. nov., C. trowbridgeae sp. nov., C. blackburnae sp. nov., C. tutela sp. nov., C. basi sp. nov., C. whaapi sp. nov., C. goodheartae sp. nov., and C. liliuokalaniae sp. nov.). The 10th species, from the Red Sea, is not named due to the absence of internal anatomical data. These findings increase the species richness in Cyerce by about two-thirds, and demonstrate that even conspicuous taxa harbour considerable cryptic diversity.