Digestive tract morphology and metallocarboxypeptidase M14 gene family divergence associated with trophic niche differentiation in Odontodactylus japonicus, Lysiosquilla sulcirostris and Oratosquilla oratoria

Stomatopods may have evolved divergent trophic niches during adaptive radiation, yet the morphological and molecular bases underlying this diversification remain poorly understood. Here, we integrated multi-level microscopic observations with full-length (FL) transcriptome data to compare digestive-tract morphology and metallocarboxypeptidase M14 ( MCP M14 ) characteristics among Odontodactylus japonicus , Lysiosquilla sulcirostris and Oratosquilla oratoria . The FL transcriptome of L. sulcirostris was newly generated in this study, whereas those of O. japonicus and O. oratoria were obtained from previously published datasets. Pronounced interspecific differences were observed in digestive morphology. O. oratoria exhibited the highest density of cardiac-stomach setae and the narrowest gland-filter pores, whereas L. sulcirostris had the thickest cardiac-stomach wall and chitin layer and the most developed pyloric muscular layer. In contrast, O. japonicus showed the greatest hindgut villus height and hepatopancreas index. Using the newly generated FL transcriptome of L. sulcirostris and previously published datasets for O. japonicus and O. oratoria , we identified 45 MCP M14 sequences in O. japonicus , 26 in L. sulcirostris and 15 in O. oratoria . MCP M14 sequences from O. japonicus and L. sulcirostris were assigned to the M14A, M14B and M14D subfamilies, whereas only M14A sequences were detected in O. oratoria . Conserved-motif and sequence analyses indicated overall structural conservation but substantial variation in subfamily composition and canonical catalytic residues. Integrative analysis further revealed distinct morphological–molecular profiles, with O. japonicus showing greater hindgut villus development and a broader detected MCP M14 repertoire, L. sulcirostris displaying greater specialization in mechanical food processing, and O. oratoria exhibiting more pronounced filtration-related traits. These findings indicate that digestive adaptation among the three stomatopods is associated with distinct combinations of digestive morphology and MCP M14 characteristics rather than uniform changes across the digestive system. Such contrasting morphological–molecular configurations provide an integrated basis for understanding trophic niche differentiation in stomatopods.