A synopsis of Macrobrachium Spence Bate, 1868 (Decapoda: Caridea: Palaemonidae) from Hong Kong, with description of a new species

Only four freshwater shrimp species from the genus Macrobrachium are known previously from Hong Kong, namely M. formosense, M. hainanense (), M. meridionale, and M. nipponense (De Haan, 1849). This is likely an underestimate as a result of insufficient sampling, given that recent efforts revealed several new records in their counterpart family Atyidae, and the presence of many more Macrobrachium species from the region (i.e., Guangdong Province, China). We report the occurrence of three more species in Hong Kong: M. equidens (), M. lar (), M. venustum (), and a new species being described, M. lantausp. nov. The new species is erected from the highly variable M. equidens species complex, distinctive in live colouration and genetics. Decisive morphological differences from M. equidens sensu lato could not be confidently elucidated until the species complex is fully resolved. Molecular analysis shows that 'M. hainanense' reported from Hong Kong actually refers to M. laevis. Morphological (and molecular) evidence suggest that M. inflatum and M. superbum () are possibly morphotypes and thus synonyms of M. nipponense. Macrobrachium hainanense and M. heterorhynchos are also likely synonyms of M. formosense and M. equidens, respectively. These species are, nevertheless, maintained as valid until examination of the type specimens concurs. The importance of an integrative approach and the associated matters needing attention in systematic studies of Macrobrachium are discussed.