A new species of the genus Gammarus Fabricius, 1775 is described and illustrated from the Tian Shan, China. Gammarus liuruiyui sp. nov. is characterized by eyes being absent; pereopods V-VII bases not expanded; uropod III with scale-like inner ramus, second article of outer ramus vestigial; and posterior margins of epimeral plates nearly straight. Detailed morphological comparisons with related species are discussed. Genetic distances of the new species and related species are provided as proof of the species delimitation.

Marine-terrestrial transition represents an important aspect of organismal evolution that requires numerous morphological and genetic innovations and has been hypothesized to be caused by geological changes. We used talitrid crustaceans with marine-coastal-montane extant species at a global scale to investigate the marine origination and terrestrial adaptation. Using genomic data, we demonstrated that marine ancestors repeatedly colonized montane terrestrial habitats during the Oligocene to Miocene. Biological transitions were well correlated with plate collisions or volcanic island formation, and top-down cladogenesis was observed on the basis of a positive relationship between ancestral habitat elevation and divergence time for montane lineages. We detected convergent variations of convoluted gills and convergent evolution of SMC3 associated with montane transitions. Moreover, using CRISPR-Cas9 mutagenesis, we proposed that SMC3 potentially regulates the development of exites, such as talitrid gills. Our results provide a living model for understanding biological innovations and related genetic regulatory mechanisms associated with marine-terrestrial transitions.

Myanmarorchestia victoria sp. nov. is described from high altitude habitats in Myanmar. The new species differs morphologically from its congeners by palp of maxilliped narrow; sexually dimorphic gnathopod Ⅱ, propodus of male chelate and propodus of female mitten-shaped; and dimorphic uropod Ⅱ, outer ramus of male with small teeth distally, outer ramus of female with three distal spines. Analysis of DNA barcode sequences and niche distinctiveness support recognition of the new species.