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Genetic and Morphological Analyses Reveal Pseudocryptic Speciation of Micromelo Undatus Bruguière, 1792
Micromelo undatus (Bruguière, 1792), represents the only species in the genus Micromelo (Family Aplustridae). This species of "bubble snail" is generally found in warm, tropical and subtropical waters across the globe. Recent work on other globally distributed sea slug taxa has shown a repeated pattern of previously unrecognized diversity. This study examines different populations across the range of Micromelo and builds a molecular phylogeny using two mitochondrial genes (16S and CO1) and one nuclear gene (H3) revealing that M. undatus is a species complex of four species. Molecular and morphological analyses show consistent genetic and anatomical differences among each of the four species. Based on literature review and evaluation of type material, available names exist for three of the four recovered species. Micromelo guamensis, Micromelo nitidulus and Micromelo eximius are resurrected for the species found in the Southwestern Pacific, the Atlantic Ocean, and the Indo-Pacific, respectively. Studying Micromelo has allowed us to make hypotheses about the importance of several factors that may play a role in speciation and diversity in benthic marine organisms. For example, biogeographical patterns such as fluctuation in sea level, particularly in the Coral Triangle, may have isolated populations and prevented gene flow leading to speciation. Recognizing patterns of speciation in basal lineages such as this can provide insight into the mechanisms of evolution undergone by other marine species with similar biogeographic distributions. Further understanding of the ecology of this genus such as larval developmental modes, feeding preferences, and reproductive strategies are required in order to further examine important factors that may play a role in speciation.