| Summary: | In this paper, three species of the macrostomid free-living flatworm genus Macrostomum are described. Two species, Macrostomum littorale Wang & Shi, sp. nov. and M. shekouense Wang & Shi, sp. nov., were collected from coastal water at Shenzhen, Guangdong Province, China. One species, M. brandi Wang & Shi, sp. nov., was collected from Perth, Western Australia and Queenscliff, Victoria, Australia. Macrostomum littorale sp. nov. differs from congeneric species within the genus in the length of the stylet, diameter of stylet opening, and the bend of the stylet. Macrostomum shekouense sp. nov. and M. brandi sp. nov. differ from similar species within the genus in the stylet morphology, position of the female antrum and developing eggs, or presence or absence of the false seminal vesicle. Phylogenetic analysis based on cytochrome c oxidase subunit I (COI) gene shows that M. littorale sp. nov. and M. hystrix are sister clades on two well-separated branch, M. shekouense sp. nov. and M. brandi sp. nov. are sister clades on two well-separated branches. Accordingly, both morphological and molecular evidence support M. littorale sp. nov., M. shekouense sp. nov., and M. brandi sp. nov. as three new species.
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