A new discovery of cryptic species in barred sand burrower Limnichthys fasciatus (Pisces: Creediidae) from the western Pacific, with evolutionary perspectives of anti-equatorial species.

Although the barred sand burrower, Limnichthys fasciatus, is widely distributed throughout the western Pacific, including Japan, Taiwan, and Australia, its morphology and genetics are poorly known. We discovered four cryptic species of Limnichthys from the western Pacific based on mtDNA cytochrome c oxidase subunit I (COI) and 16S ribosomal RNA (rRNA) sequences. Genetic distances showed remarkably large differences (12.7%-24.3% in COI and 7.9%-19.6% in 16S rRNA) between true L. fasciatus (type locality: southeastern Australia) and the others. A relaxed clock model with optimized selected substitution models showed that their deep divergence began in the middle Miocene epoch and subsequently diverged into the current cryptic species in the Plio-Pleistocene. A eurythermal common ancestor may have evolved independently in each region due to geographical events and paleoclimatic fluctuations, which made it possible for L. fasciatus complex to be an anti-equatorial species. Despite their deep genetic divergence, they showed marked phenotypic similarity, suggesting that they have experienced similar selective pressures related to their specific behavior.