The evolutionary and genetic origins of the specialized body plan of flatfish are largely unclear. We analyzed the genomes of 11 flatfish species representing 9 of the 14 Pleuronectiforme families and conclude that Pleuronectoidei and Psettodoidei do not form a monophyletic group, suggesting independent origins from different percoid ancestors. Genomic and transcriptomic data indicate that genes related to WNT and retinoic acid pathways, hampered musculature and reduced lipids might have functioned in the evolution of the specialized body plan of Pleuronectoidei. Evolution of Psettodoidei involved similar but not identical genes. Our work provides valuable resources and insights for understanding the genetic origins of the unusual body plan of flatfishes.

Konosirus punctatus inhabits areas of significant commercial importance in Chinese coastal waters. Twelve populations distributed all along the Chinese coast were analyzed using two mtDNA genes. The cytochrome oxidase subunit I (COI) and cytochrome b (Cytb) genes were amplified from 242 and 259 individuals, respectively, and fragments of 999 and 415 bp sequence in length were used for analysis. COI and Cytb denoted a high haplotype diversity and low nucleotide diversity. The COI mtDNA gene revealed a high molecular variance within populations and low variance among populations, whereas Cytb showed a high variance among populations and low within populations. F_ST values obtained for COI and Cytb showed low genetic differentiation among the populations, except for the Zhongshan population where the Cytb gene showed high F_ST values. The constructed phylogenetic tree and haplotype network tree showed a single lineage, however, Cytb gene data showed that the Zhongshan population has a greater difference level within a population. The present investigation contributed to existing knowledge of the genetic structure of K. punctatus and can be useful for its future conservation.