The kuruma shrimp Penaeus japonicus is widely distributed throughout the Indo-West Pacific (IWP) and is of economic importance in shrimp fisheries in many areas.It is also the first penaeid species developed for aquaculture, and is now cultured in Japan, Australia and many Southeast Asian countries.P.japonicas is characterized by the diagnostic pouch-like thelycum.While its taxonomy has been relatively uncontroversial, we have recognized two morphologically similar colored forms from the South China Sea.Both Form Ⅰ and Form Ⅱ do not exhibit any diagnostic differences in morphological or morphometric traits, and are only distinguishable by specific color banding patterns on the carapace.Analyses of mitochondrial (mt) DNA and amplified fragment length polymorphism (AFLP) concordantly reveal that the two forms are genetically differentiated.The absence of genetic exchange between the forms is demonstrated by the lack of shared mtDNA haplotypes and of hybridization in AFLP analysis.Phylogenetic analyses of both markers further demonstrate that these two forms are more closely related to each other than to other Penaeus species.All these findings are consistent with the presence of cryptic species in the kuruma shrimp.Investigation on the population structure of the shrimps over IWP using mtDNA and microsatellite markers reveal that Form Ⅰ only occurs in Japan and China (including Taiwan), whereas Form Ⅱ is widely distributed in Southeast Asia, Australia, Indian Ocean, Red Sea and Mediterranean Sea.As the type locality ofP.japonicus is Japan, Form Ⅰ is the nominotypical form.A rarely used name P.pulchricaudatus is described as a junior synonym of P.japonicus from the east coast of South Africa, yet the only single and century-old specimen is a sexually undetermined juvenile which does not provide enough diagnostic evidence to distinguish it from other closely related species.A new name must be established for Form Ⅱ and the nomenclature of this newly defined cryptic species will be revised soon.Moreover, the differences in the biology of the two forms should be scrutinized for academic, fishery and aquaculture purposes.For instance, difference in temperature tolerance has been reported in the shrimps collected from different areas and may represent species difference.An exhaustive literature review on the kuruma shrimp is underway in order to dissect differences in various biological attributes between the two colored forms.Such information is crucial for the fishery management and aquaculture development of this commercially important shrimp.