BackgroundIt has been suggested that aquaculture ponds on the Chinese coast could act as breeding grounds for scyphozoans. Here, we present the first record of the scyphomedusaPhyllorhizasp. in an aquaculture pond on the coast of the southern Yellow Sea, based on a combination of morphological characteristics and mitochondrial 16S DNA sequence data.MethodsA field survey was performed on June 29, 2017 in a pond used for culturing the shrimpPenaeus japonicus, located in the southern Yellow Sea, China. Jellyfish specimens were collected for morphological and genetic analysis. The morphological characters of the jellyfish specimens were compared to taxonomic literature. Additionally, phylogenetic analysis of the mitochondrial 16S fragments of these specimens were also conducted.ResultsThese specimens had the following morphological characters: hemispherical umbrella without scapulets; J-shaped oral arms; a single larger terminal club on each arm; bluish colored with a slightly expanded white tip; and mouthlets present only in the lower half to one-third of each arm. These morphological features of the medusae indicated that the specimens found in the shrimp culture ponds belong to the genusPhyllorhizaAgassiz, 1862, but did not match with the description of any of the known species of the genusPhyllorhiza.Phylogenetic analyses of the mtDNA 16S regions revealed that these specimens, together withPhyllorhizasp. from Malaysian coastal waters, belong to a sister group ofPhyllorhiza punctata. Juveniles and ephyrae ofPhyllorhizasp. were observed in the aquaculture pond. The mean density ofPhyllorhizasp. medusa in the surface water within the pond was estimated to be 0.05 individuals/m2.DiscussionBased on our observations of the gross morphology and molecular data, we state that the specimens collected in the aquaculture pond can be identified asPhyllorhizasp. This is the first record ofPhyllorhizasp. in Chinese seas. Large scale dispersal through ballast water or the expansion of jellyfish aquarium exhibitions are possible pathways of invasion, but this needs to be confirmed in further studies.