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The aim of this study was to describe a new species of Didymozoidae (Trematoda) found in the mesentery of Euthynnus alletteratus (Rafinesque) off Cabo Frio, in the coastal area of the state of Rio de Janeiro, Brazil. Thirty specimens of E. alletteratus were obtained between August 2023 and June 2024, directly from traders who sell fresh fish in markets. The parasites were fixed in AFA (93% ethanol 70%, 5% formaldehyde and 2% glacial acetic acid) with or without compression, stained with Langeron's hydrochloric carmine, dehydrated in an alcohol series, clarified in clove oil and mounted in Canada balsam as permanent slides. The new species was assigned to the genus Lobatozoum Ishii, 1935, mainly by the presence of lobes in the posterior region of the body and by the arrangement of the testes, ovary and vitellaria. Lobatozoum woodi n. sp. differs from all congeneric species mainly by presenting three testicular tubules, by the size of pharynx, larger than the oral sucker, and by the absence of digestive glands cells in esophagus and initial portion of caeca. The finding of a new species of Lobatozoum represents the eleventh valid species in the genus.