AI‐Assisted Morphometric Analysis and Molecular Phylogeny for a Dactylogyrid (Monopisthocotyla) Skin Parasite of an Ornamental Crenuchid Fish From Brazil

This study presents a formal description and taxonomic appraisal of Cacatuocotyle adrianoi sp. n., a Neotropical parasite belonging to the family Dactylogyridae, integrating AI‐assisted morphometric analyses, molecular data, and phylogenetic reconstruction. Phylogenetic analyses recovered Cacatuocotyle adrianoi sp. n. within a strongly supported clade as sister to all other congeners, supporting the hypothesis that Cacatuocotyle independently underwent a secondary loss of a pair of anchors, given its distant phylogenetic position relative to Dactylogyrus spp. Genetic divergence based on 28S rDNA ranged from 7% to 11% among congeners, whereas COI sequences displayed even higher disparity (19%). Morphological and AI‐assisted morphometric comparisons between specimens of Cacatuocotyle adrianoi sp. n., collected from the skin of Characidium zebra in the Tietê River Basin (São Paulo State), and those of the type species C. paranaensis , recovered from Characidium lanei in the Cacatu River (Paraná State—type host and type locality), revealed consistent differentiation between populations. The best‐performing models achieved correct prediction rates of 90.9%–91.3%, slightly below the ≥ 93% threshold conventionally adopted for species delimitation in Dactylogyridae, yet still lending support to our taxonomic conclusions. Direct molecular comparisons were constrained, however, by the absence of sequence data from topotypic specimens of C. paranaensis . Collectively, these results underscore the value of integrative, phylogenetically grounded taxonomic frameworks, especially for parasitic taxa prone to morphological plasticity and cryptic speciation.