Objective:To examine the taxonomic boundaries in the Stellantchasmus populations in different hosts and reveal the cryptic speciation of the Stellantchasmus in Thailand based on both morphological and molecular approaches.Methods:Stellantchasmus falcatus(S.falcatus) s.l.was collected from different hosts throughout Thailand.The worms were examined and measured.The nuclear ITS2 gene and the mitochondrial COI gene were used to investigate the S.falcatus s.l.from Dermogenus pusillus and Liza subviridis.Results:Stellantchasmus was one of food-borne trematode that widely distribute throughout Thailand.The comparison of S.falcatus s.l.from Dermogenus pusillus and Liza subviridis indicated a genetic divergence of nuD NA with 3.6% and mtD NA with 19.3%,respectively.Morphological characteristics were fairly different in the ratio of body size,length of prepharynx,and ratio of organ size.Conclusions:Our results provide initial evidence that S.falcatus s.l.from different hosts tend to be a different species based on both molecular and morphological characters.Cryptic species complexes are generally found among parasites that tend to have large populations and/or rapid evolution.The degree of genetic diversity existing would suggest the practice of targeted regimes to design and minimize these lections of anthelmintic resistance in the future. Objective: To examine the taxonomic boundaries in the Stellantchasmus populations in different hosts and reveal the cryptic speciation of the Stellantchasmus in Thailand based on both morphological and molecular approaches. Methods: Stellantchasmus falcatus (S.falcatus) slwas collected from different hosts throughout Thailand. The worms were examined and measured. The nuclear ITS2 gene and the mitochondrial COI gene were used to investigate the S. falcatus slfrom Dermogenus pusillus and Liza subviridis. Results: Stellantchasmus was one of food-borne trematode that were widely distributed throughout Thailand. Comparison of S.falcatus slfrom Dermogenus pusillus and Liza subviridis indicated a genetic divergence of nuD NA with 3.6% and mtD NA with 19.3%, respectively.Morphological characteristics were fairly different in the ratio of body size, length of prepharynx, and ratio of organ size.Conclusions: Our results provide initial evidence that S.falcatus slfrom different hosts tend to be a differ ent species based on both molecular and morphological characters. Cryptic species complexes are generally found among parasites that tend to have large populations and / or rapid evolution. The degree of genetic diversity existing would suggest the practice of targeted regimes to design and minimize these lections of anthelmintic resistance in the future.