Complete Mitochondrial Genome of Acartiella sinensis Shen & Lee, 1963 (Copepoda, Calanoida) and Its Phylogeny

Acartiidae are often among the most dominant and ecologically critical copepod groups in estuarine pelagic food webs. Here, we sequenced and characterized the complete mitochondrial genome of Acartiella sinensis, representing the first mitogenome for the family Acartiidae. The circular genome is 14,368 bp in length and exhibits a strong A+T bias (79.7%) and a compact organization, with all genes encoded on the heavy strand. Codon usage exhibits a preference for A/U-ending codons, while tRNA secondary structure analysis reveals two serine tRNAs lacking DHU arms and several G–U mismatches. Comparative analysis across 29 copepod mitogenomes indicates a distinctive gene arrangement in A. sinensis, particularly a reversal of Cytb and NAD3 with local tRNA rearrangements. Phylogenetic analyses based on concatenated sequences of 13 protein-coding genes recover A. sinensis as sister to the clade comprising Labidocera rotunda (Pontellidae) and Eurytemora affinis (Temoridae), supporting close evolutionary relationships among these calanoid lineages. Our study provides fundamental genomic information for A. sinensis and contributes to the understanding of mitochondrial genome evolution and phylogenetic relationships within Calanoida.