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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. 

ABSTRACT AimThuridillaBergh, 1872, is a lineage of herbivorous sea slugs externally distinguished by bright colours and distinctive patterns of lines and spots. Recent work revealed an exceptionally rapid, cryptic radiation of 13 species in the Indo‐Pacific, raising questions about mechanisms of speciation in this group. Here, we (i) study the diversification and historical biogeography ofThuridillain a phylogenetic context and (ii) assess the role of dispersal and vicariance as the predominant mode of speciation in the genus. LocationTropical and temperate regions of the Atlantic and Indo‐Pacific. Major Taxa StudiesGastropoda, Sacoglossa. MethodsA nearly complete taxon set with 28 out of 32 recognised species ofThuridillawas used, in a total sample of 172 specimens, together with sacoglossan outgroups. Phylogenetic relationships were determined using a multi‐locus approach combining two mitochondrial (COI and 16S) and one nuclear gene (H3). Species relationships, diversification times, and ancestral geographical ranges were inferred using relaxed‐clock methods together with Bayesian discrete phylogeographic methods under three calibration scenarios using the oldest known fossil of Sacoglossa,Berthelinia elegansCrosse, 1875, and tectonic events. ResultsThuridillaspecies branched off into four major clades in all calibration scenarios: two groups from the Atlantic plus Indo‐West Pacific (5 and 6 species) and two clades from the Indo‐West Pacific (4 and 17 species). The highest diversity of the genus is in the Western Pacific (14 spp.) with a peak in the East Indies Triangle (18 spp.), whereas the Atlantic is depauperate with only four species occurring in this ocean basin. Divergence between Atlantic and Indo‐West Pacific lineages occurred in two main temporal periods: the Miocene and the Pliocene. Speciation events within the 13 cryptic species‐complex fell mostly within Plio‐Pleistocene times. Main ConclusionsThe best supported hypothesis was an Indo‐West Pacific origin ofThuridillabetween 28 and 18 Mya during the Early Miocene. In the western Pacific, speciation likely occurred during transient allopatry during Plio‐Pleistocene sea‐level fluctuations. Under the three tested calibration scenarios, the limited diversity of the Atlantic Ocean is hypothesized to be derived from Miocene vicariant events associated with the closure of the Tethys Sea, dispersal across southern Africa, or long‐distance dispersal across the East Pacific Barrier prior to the uplift of the Isthmus of Panama.Thuridillais absent in the Eastern Pacific, potentially resulting from the extinction of ancestral lineages following the uplift of the Isthmus of Panama. Near‐complete sampling of diversity and reconstruction of historical biogeography thus yielded new insight into the relative contributions of dispersal versus vicariance during speciation over the history of this widely distributed, colourful genus.