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Phylogenetic Systematics of the Sea Slug Genus Cyerce Bergh, 1871 Using Molecular and Morphological Data
The genus Cyerce Bergh 1871 is a group of heterobranch sea slugs in the family Caliphyllidae, characterized as having bifid rhinophores, enrolled oral tentacles, multiple leaf-like cerata, and a transverse groove splitting the foot sole of the animal transversally. Cyerce currently includes eight to eleven accepted species distributed throughout tropical and subtropical areas of the Indo-West Pacific, Eastern Pacific, Northern Atlantic, Caribbean, and Mediterranean. Species of Cyerce are stenotropic herbivores that possess remarkable adaptations, such as aposematic coloration, synthesis of polypropionates, and acquisition of plastids from their algal hosts. The evolution of these traits in Cyerce has not been studied, although observed in other lineages within Sacoglossa. Cladistic analyses have been performed on Sacoglossa, but species level phylogenetic analyses for the genus Cyerce are lacking. Morphological studies have been used to distinguish species of Cyerce in past studies, but the evolutionary relationships among these species remain undetermined. The objective of this study is to produce a monographic review of the genus Cyerce using both molecular and morphological data. In order to resolve the evolutionary relationships among Cyerce species, two mitochondrial genes (CO1, 16S) and a nuclear gene (H3) were sequenced from one hundred and fifty-four specimens loaned from museums or collected in the field. Bayesian and Maximum Likelihood analysis were used to generate phylogenetic trees. A species delimitation analysis with ABGD was performed using CO1 aligned sequences to delineate species among the clades recovered in the phylogenetic analyses. The internal anatomy of the Cyerce specimens was studied to supplement molecular data. This included dissections of the radula and male reproductive anatomy. A literature review was further conducted to investigate the validity of species. Twenty-four genetically distinct species of Cyerce were recovered from the analyses with diagnostic in differences penial and radular morphology between species. This study also resulted in novel findings, such as evidence of fifteen new species of Cyerce. From the fifteen new species, several belong to cryptic and pseudocryptic species complexes that, without the integration of molecular and morphological data, would not have been discovered.