Two new species of the genus Allocreadium were isolated from the intestines of the Lake minnow Rhynchocypris percnura caught in the backwater of the Komissarovka River in the South of the Russian Far East. The morphology of A. anastasii n. sp. corresponds to that of Allocreadium sp. from Lake Khar (Mongolia) and Allocreadium sp. Belous, 1952 from the Primorsky region of Russia except for the preacetabular anterior border of the vitelline follicles in A. anastasii n. sp. from the Komissarovka River vs. at anterior half of ventral sucker in Allocreadium sp. Genetic analysis revealed the identity of A. anastasii n. sp. to Allocreadium sp. 1 from the Nezhinka River and Lake Khar. Allocreadium macrolecithum n. sp. was differentiated from Palaearctic Allocreadium spp. by having the following features: respectively large vitelline follicles extending from posterior extremity to anterior margin of the ventral sucker; relatively short caeca reaching the border of middle and posterior thirds of hindbody; and small testes in the middle of hindbody. Interspecific genetic p-distances between Allocreadium spp. were 0.16–7.23% in 28S gene and 18.62–31.54% in Cox1 mtDNA gene. In the phylogenetic tree reconstructed with Maximum parsimony and Bayesian Inference methods, A. anastasii n. sp. and A. macrolecithum n. sp. were nested into different species groups of the genus Allocreadium – sister to A. khankaiense and A. bursense, respectively. Modified dichotomous keys were prepared for 31 Palaearctic species of Allocreadium including A. crassum, A. dogieli, A. papilligerum, A. bursense, A. anastasii n. sp., and A. macrolecithum n. sp.

This is the first study reporting parasites from the freshwater cyprinid Oxynoemacheilus angorae (Steindachner 1897) caught in Nilüfer Stream, Bursa, in the Northwest Anatolian Region of Turkey. Allocreadium bursensis n. sp. was described from the intesine of O.angorae based on morphological and genetic characteristics. Allocreadium bursensis n. sp. was differentiated from other Allocreadium spp. in having a combination of external (ventral and oral suckers ratio; body length and width and its ratio to forebody) and internal (cirrus pouch position; uterus extension in hindbody; egg size; disposition of anterior border of vitellarium; esophagus length) features. Phylogenetic hypotheses based on maximum parsimony, maximum likelihood, Bayesian inferrence, and neighbor joining analyses of sequence data strongly supported the hypothesis that A. bursensis is nested within the clade of Allocreadium species hosted by cypriniform fish, and it is more closely related to the Far Eastern species A. pseudoisoporum (Primorsky region, Russia) than to the African A. apokryfi. According to genetic p-distances, the taxonomic status of trematodes collected in Turkey was established as independent relative to nine of the valid Allocreadium spp.: 1.8–5.8% in 28S gene and 18.8–22.6% in cox1 gene. The present study increases the number of Allocreadium species and their definitive hosts recorded in Turkey and raises the number of Palearctic representatives of Allocreadium spp. to 26.

Cosmetocleithrum Kritsky, Thatcher & Boeger, 1986 (Dactylogyridae) represents one of the most species-rich groups (22 species currently recognized as valid) of all dactylogyrid parasites infecting Neotropical catfishes. Species of Cosmetocleithrum exhibit a remarkable affinity towards catfishes of the Doradidae and the Auchenipteridae. However, phylogenetic relationships between members of this genus have not been yet analysed. This study analysed newly obtained partial sequences of the 28S ribosomal RNA gene of seven species of Cosmetocleithrum, including its type species C. gussevi Kritsky, Thatcher & Boeger, 1986, along with several other dactylogyrids infecting siluriform, gymnotiform, perciform and characiform fishes. Cosmetocleithrum appeared as an evolutionary recent group, composed of two well-defined lineages: lineage 1 includes parasites of doradids – namely, C. bulbocirrus, C. confusum, C. parvum and C. bifurcum – whereas lineage 2 is composed of species from doradids – that is, C. rarum, C. gussevi, C. gigas, C. trachydorasi and C. falsunilatum – together with parasites of auchenipterids – namely, C. laciniatum and C. baculum. The search for synapomorphies to characterize taxonomic groups within Cosmetocleithrum appears challenging, since the morphology of their haptoral elements is quite conservative, and that of the copulatory complex is highly variable between species. The results of the present study support the recent synonymization of Paracosmetocleithrum Acosta, Scholz, Blasco-Costa, Alves & Silva, 2018 with Cosmetocleithrum. Whereas the 28S ribosomal DNA data resolved Cosmetocleithrum as monophyletic, the statistical support for the lineage was low, rendering its phylogenetic position between other Neotropical dactylogyrids yet undefined.