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ABSTRACT In this paper, a new genus in the nudibranch family Discodorididae, Avaldesia n. gen., is established for Avaldesia albomacula (Chan & Gosliner, 2007) and Avaldesia tahala (Chan & Gosliner, 2007), originally assigned to the genus Thordisa Bergh, 1877, and a new species, Avaldesia tamatoa n. sp., described here from the central Pacific. To establish species relationships within Avaldesia, as well as the placement of Avaldesia within Discodorididae, we utilized four molecular markers (cytochrome c oxidase subunit I, 16S rRNA, histone H3 and 28S rRNA) in our Bayesian inference and maximum likelihood analyses. Four species delimitation methods were complemented by morphological dissections and scanning electron microscopy. Our results reveal a clear separation between Avaldesia and Thordisa and suggest that Avaldesia is more closely related to the genera Hoplodoris Bergh, 1880 and Asteronotus Ehrenberg, 1831. The most characteristic features of Avaldesia include a radula with increasing denticulation towards the fimbriate outermost laterals and a reproductive system with a lobate vestibular gland, occasional hollow vestibular spine and a penis armed with one or more penial spines. All species of Avaldesia are found in shallow water (5–10 m depth) on rocky reefs, sandy sediments and algal fields with distributions across the Indo-Pacific. 

The Chromodorididae family tree has been refined in recent years via molecular phylogenetic analyses which have clarified many relationships between taxa. The genus Goniobranchus is one clade within Chromodorididae that was previously included within the genus Chromodoris. However, based on recent molecular phylogenetic results, Chromodoris was determined to be non-monophyletic and Goniobranchus was resurrected. In this study, we performed molecular and morphological analyses to resolve the internal relationships among Goniobranchus species, specifically the red-reticulate species complex of three previously described species, Goniobranchus tinctorius, G. reticulatus, and G. alderi, which display a red network of lines over a white mantle and are widely distributed across the Indo-Pacific Ocean. We sequenced two mitochondrial genes (COI and 16S) and one nuclear gene (H3) for 339 Goniobranchus specimens, and in our phylogenetic analyses the red-reticulate species group emerged as a monophyly. This current work has indicated there are at least eleven distinct species within this species complex, including the only three previously described species and another described species, G. splendidus, was added to this clade. The molecular data and the morphological differences among species will be discussed, and we present a possible way forward to clarify the taxonomy of the red-reticulate species complex. 

Expeditionary field work still remains the most fundamental tool to discover novel species and repetitive sampling in high diversity portions of the Indo-Pacific tropics continues to provide large numbers of previously undocumented taxa. Multidisciplinary collaborative teams and large expeditions are an immense source of novel biodiversity. Micro-scale temporal changes in diverse ecosystems provide a catalyst for new species discovery, as well as insights into the discovery of patterns of trophic and symbiotic divergence. Additionally, phylogenetic analyses of large samples of diverse taxa across geographical gradients have increasingly detected cryptic and pseudo-cryptic species complexes that have dramatically altered our view of species richness. Aposematic and extreme camouflaged colour patterns within the context of fish predatory behaviour provides an evolutionary framework for divergence and convergence of colour patterns. Similarly, recent studies of temperate nudibranch assemblages in temperate waters in Europe, southern Africa and the Pacific coast of North America also demonstrate previously undetected diversity and the presence of colour patterns that likely reflect similarity derived from both common ancestry and convergence. Combining these approaches has documented astonishingly high levels of previously undetected diversity, has huge implications to our knowledge of global biodiversity with a likely 3-5x increase in global species richness, and has developed more appropriate regenerative conservation strategies.