The diversity of <i>Khawia</i> tapeworms (Cestoda: Caryophyllidea) of barbels (Cyprinidae: Barbinae) in the western Palearctic: the existence of vicariant lineages and the description of a new species from the Iberian Peninsula

The caryophyllidean tapeworm <i>Khawia armeniaca</i> has long been regarded as an exceptionally widespread species within its genus, notable for its significant morphological variability. However, with the accumulation of molecular data from different fish hosts, <i>K. armeniaca</i> was suspected to represent a species complex. To clarify the true identity of these parasites, a comprehensive morphological and molecular study (using 18S, 28S and ITS2 ribosomal regions) of <i>K. armeniaca</i> tapeworms from barbels (Barbinae) across the Iberian Peninsula and the Middle East has been conducted. The results revealed two genetically distinct lineages within the <i>K. armeniaca</i> complex. The first lineage, found in <i>Arabibarbus grypus, Barbus lacerta, Capoeta birunii, Carassobarbus luteus, Luciobarbus barbulus, L. esocinus</i> and <i>L. kersin</i> in Iraq and Iran, is genetically congruent with <i>K. armeniaca</i> (Cholodkovsky, 1915), originally described from the Sevan khramulya (<i>Capoeta sevangi</i>) in Armenia. The second lineage, identified in <i>Luciobarbus bocagei</i> (type host), <i>L. comizo</i> and <i>L. guiraonis</i> from Portugal and Spain, is described as <i>Khawia iberica</i> n. sp. In addition to clear molecular divergence, <i>K. iberica</i> can be distinguished from <i>K. armeniaca</i> by notable morphological differences, including variations in the shape, structure and size of the ovary, the anterior extension of the vitelline follicles, the testes and several morphometric parameters.