<p><i>Clestobothrium crassiceps</i> (Rudolphi, 1819) Lühe, 1899 is the type species of the genus <i>Clestobothrium</i> Lühe, 1899, originally described from <i>Merluccius merluccius</i> (Linnaeus, 1758) in the Mediterranean Sea. Despite its apparently wide host and geographic ranges, this species remains poorly understood due to the lack of detailed morphological, genetic and epidemiological data. In the present study, newly collected materials of <i>C. crassiceps</i> from <i>M. merluccius</i> off Barcelona, Spain (NW Mediterranean) were used to provide the first complete description from its type-host and locality. An integrative approach was applied, combining traditional morphological techniques with confocal laser scanning microscopy (CLSM), scanning electron microscopy (SEM), molecular, histological and epidemiological data. Confocal microscopy revealed key diagnostic features of the female reproductive system (<i>i.e.</i> vagina, Mehli’s gland, uterus tube), while SEM analysis showed, for the first time, different distribution patterns of microtriches along the scolex and strobila. Histological observations showed the attachment mode of the scolex to intestinal folds, causing mild epithelial alterations such as attenuation of the intestinal epithelium. Prevalence and intensity of infestation with <i>C. crassiceps</i> were higher in larger fish, suggesting a role for dietary shifts and potential paratenic hosts in transmission. Phylogenetic analysis based on newly generated 28S and cox1 sequences confirmed the monophyly of the genus <i>Clestobothrium</i> and highlighted an intraspecific variation comparable to the genetic divergence observed between congeners <i>C. splendidum</i> and <i>C. cristinae</i>. Based on these results, a morphological reexamination of paratypes of both species was conducted, proposing <i>C. cristinae</i> as a junior synonym of <i>C. splendidum</i>.</p>