Histological diagnosis of Lecithochirium species parasitizing Trichiurus lepturus Linnaeus, 1758 from southeastern Brazil

Abstract

Histological approaches remain underexplored in the taxonomy of marine digenean trematodes, despite their capacity to reveal internal morphological characters of diagnostic value. In this study, we provide the first detailed histological characterization and comparative analysis of two hemiurid species, Lecithochirium microstomum Chandler, 1935 and Lecithochirium monticellii (Linton, 1898), parasitizing the cutlassfish Trichiurus lepturus Linnaeus, 1758, from the southeastern Brazilian coast. Specimens were processed using classical histological techniques, enabling comprehensive examination of tegumental, muscular, digestive, and reproductive systems. Both species exhibited a syncytial tegument covered by a thin glycocalyx, well-developed oral and ventral suckers with complex fibromuscular organization, and intestinal ceca lined by a simple epithelium. The reproductive system comprised testes, a compact ovary embedded in a fibroelastic stroma, and a distinct hermaphroditic duct formed by the junction of the ejaculatory duct and the terminal portion of the uterus. Histological differentiation between species was primarily based on cirrus morphology and posterior body organization. Lecithochirium microstomum exhibited a shorter and wider cirrus and a reduced, largely internalized ecsoma, whereas L. monticellii presented a longer, more slender cirrus and a well-developed ecsoma with a greater volume of connective tissue. By documenting previously undescribed histological characters, this study establishes histology as a robust and independent source of taxonomic evidence, reinforcing its value as a complementary tool in integrative taxonomy and evolutionary studies of Hemiuridae.