Morphological phylogeny on the unnatural grouping of Demidospermus-like species (Monopisthocotyla, Dactylogyridae) with the proposal of new genera, genera resurrections, and descriptions of new species.

Dactylogyrids are flatworms of ecological and economic significance, parasitizing fish worldwide. In recent years, there has been a surge in the description of Neotropical dactylogyrids, particularly those infecting siluriform fishes. While these studies have contributed to the organization of some genera and refined species boundaries through integrative taxonomy, certain groups within the family, such as Demidospermus, remain taxonomically unstable. This study focuses on Demidospermus, aiming to reclassify species of uncertain status into appropriate genera and establish a morphological framework to support future evolutionary analyses and taxonomic revisions within the Demidospermus-like species group. Supported by morphological phylogenetic analysis, we propose the new genera Rhabdolachosus n. gen., Martorellius n. gen., Magnanchistrius n. gen., and Sicohencotyle n. gen., along with the resurrection of Omothecium Kritsky, Thatcher & Boeger, 1987, and Paramphocleithrium Suriano & Incorvaia, 1995. Additionally, two new species are described: Sicohencotyle antoniomaiai n. gen. n. sp. and Ameloblastella sakulocirra n. sp. Also, Demidospermus centromochi Mendoza-Franco & Scholz, 2009 is classified as sedis mutabilis, while D. annulus Marcotegui & Martorelli, 2011, D. brevicirrus Mendoza-Palmero et al., 2012, D. cornicinus Kritsky & Gutierrez, 1998, D. idolus Kritsky & Gutierrez, 1998, D. armostus Kritsky & Gutierrez, 1998, D. mortenthaleri Mendoza-Palmero et al., 2012, D. osteomystax Tavernari et al., 2010, D. tocantinensis Cohen et al., 2020, D. doncellae Morey et al., 2024, D. bifurcatus Justo, Martins & Cohen, 2024, D. juruaensis Justo, Martins & Cohen, 2024, and D. takemotoi Justo, Martins & Cohen, 2024 are considered incertae sedis. Lastly, Urocleidoides amazonensis Mizelle & Kritsky, 1969 remains classified as incertae sedis.