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Abstract
The complete sequence (14,751 bp) of the mitochondrial DNA (mtDNA) of the opisthobranch gastropod Placida sp. was determined using long PCR and genome-walking techniques. The genome contains 13 protein-coding genes (PCG), 2 ribosomal RNA (rRNA), 22 transfer RNA (tRNA) genes that are typical of metazoan mtDNA, and 2 lengthy noncoding regions with a total length of 1441 bp. All the tRNA genes have general secondary structures without reduced T or D stems. The mitochondrial gene arrangement of Placida sp. is almost identical to that of sea slugs, whereas the tRNA gene arrangement is different from other animals outside Sacoglossa in the Euthyneura. A phylogenetic analysis based on the mitochondrial genome of Euthyneura indicated that Placida sp. and Placida dendritica are closely related to Elysia chlorotica as a sister taxon, which strongly supports their close phylogenetic affinity.
Declaration of interest: This work was supported by Shandong Science and Technology plan project (2011GHY11528), the High-Tech Research and Development Program (863) of China (2012AA052103), the Specialized Fund for the Basic Research Operating expenses Program (20603022012004, 2010-ts-03), National Natural Science Foundation of China (41176153), Natural Science Foundation of Shandong Province (2009ZRA02075), Qingdao Municipal Science and Technology plan project (11-3-1-5-hy), National Marine Public Welfare Research Project (200805069), and the National Science & Technology Pillar Program (2008BAD95B11 and 2010BAC68B03). The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.