A description of Echinorhynchus baeri Kostylew, 1928 (Acanthocephala: Echinorhynchidae) from Salmo trutta in Turkey, with notes on synonymy, geographical origins, geological history, molecular profile, and X-ray microanalysis.

A population of Echinorhynchus baeri Kostylew, 1928 with 18-24 rows of 8-10 proboscis hooks each and long fusiform eggs measuring 95-110 × 18-22 μm collected from Salmo trutta (Salmonidae) in a branch of the Murat River in Turkey is described and specimens are designated as neotype. Specimens of two similar populations of E. baeri (E. baeri Kostylew, 1928 and E. sevani Dinnik, 1932) were previously described from Salmo ischchan in Lake Sevan, Armenia. Waters of Lake Sevan and the Murat River were previously joined during the Middle Miocene-Pliocene. The two populations from Lake Sevan and ours from Turkey had identical morphology and size eggs. The proboscis armature and eggs, among other features of our Turkish specimens, proved intermediate between E. baeri and E. sevani, thus eliminating the significance of the described differences between these two species and confirming their synonymy with priority to Echinorhynchus baeri (junior synonym: Echinorhynchus sevani Dinnik, 1932). Echinorhynchus baeri is apparently a highly variable species. The two descriptions from Lake Sevan did not include features or illustrations of females, except for references to trunk and egg size but the eggs were illustrated. Complete morphometric comparisons are made and females of the Turkish material are described for the first time. DNA sequencing (mitochondrial cytochrome oxidase subunit I gene; nuclear 18S rRNA gene) results from two available E. baeri individuals were equivocal. New features to the Acanthocephala include the presence of rootless uncalcified apical proboscis hooks studied with X-ray microanalysis.