New species and phylogenetic insights into Cosmetocleithrum (Dactylogyridae) from thorny catfishes (Doradidae), based on morphology and molecular data

The present study expands the known diversity of monogenoids parasitizing South American catfishes of the family Doradidae. Two new species of Cosmetocleithrum, C. forcepsiformis n. sp. and C. amblydorasis n. sp., are described from Amblydoras affinis in the Guamá River Basin, Brazil, increasing to 28 the number of monogenoid species parasitizing this family of siluriform fishes. In addition, new occurrences of Cosmetocleithrum akuanduba and Cosmetocleithrum bifurcum are reported from Hassar orestis in the Amazon Basin. Our phylogenetic analyses based on partial 28S rDNA sequences do not support the monophyly of Cosmetocleithrum and instead suggest the existence of two main lineages within the genus: one restricted to Doradidae and another including species parasitizing both Doradidae and Auchenipteridae. The inclusion of new taxa improves the internal phylogenetic resolution and allows the recognition of subclades supported by both morphological and molecular data. Two additional species bearing two types of haptorial hooks are identified, expanding the distribution of this character within the genus. Ornamentations of the ventral and dorsal bars observed in C. akuanduba and C. trachydorasi are recovered as shared derived traits of a well-supported subclade. Our integrative approach, combining morphology, molecular phylogeny, and the reexamination of museum specimens, underscores the underestimated diversity of Cosmetocleithrum and reinforces the need for taxonomic revision of this enigmatic genus.