Within the present study, we offer new information on the morphology, histopathology, and 18S ribosomal DNA (rDNA) sequence of Myxobolus scardinii to supplement and revise the original description of Reuss (Bull Acad Imp Sci St-P,tersbourg, V Serie, XXV, No. 3: 199-205, 1906). M. scardinii was found infecting the gills of 6 of 125 specimens (4.8 %) of Scardinius erythrophthalmus from northern Turkey. Large mature plasmodia, whitish, spherical, or ellipsoidal, measuring 0.9-1.0 mm in diameter, macroscopically occurred in the gills. Histopathological examination indicated that development of the cyst-like plasmodia was intrafilamental-vascular type. Mature spores are oval or shortly ellipsoidal. The spores are 12.1 +/- 0.2 (11.5-12.6) mu m long, 8.9 +/- 0.3 (8.4-9.2) mu m wide, and 6.1 +/- 0.3 (5.9-6.2) mu m thick. The two polar capsules are equal in size, 4.8 +/- 0.2 (4.7-5.1) mu m long and 2.8 +/- 0.2 (2.7-3.1) mu m wide, and are long pyriform in shape. A well-developed intercapsular appendix was found in the fresh spores. In this study, a specific gill myxosporean of S. erythrophthalmus, M. scardinii the identity of which was confirmed by careful morphological and histopathological examination, was sequenced with its 18S rDNA sequence for the first time and submitted to Genbank database (accession number KJ562362). Phylogenetic analysis of the 18S rDNA gene revealed that M. scardinii had the closest similarity to M. muelleri and M. bramae. This is the first molecular data for the validity of M. scardinii in S. erythrophthalmus. This new valid genetic data (KJ562362) has been used to establish phylogenetic relationships with other similar gills Myxobolus species from Eurasia.