Systematic and phylogenetic insights into Neocalceostomatidae (Dactylogyridea): A new species, the first neotropical record of species of Neocalceostomoides and Neocalceostoma, and the redescription of Calceostomella herzbergii.

Neocalceostomatidae comprises a small group of monogenoids parasitizing marine catfishes (Siluriformes, Ariidae), with species reported exclusively from the Australian and Oriental regions. Despite their taxonomic relevance within Dactylogyridea, the evolutionary relationships within the group remain uncertain. In this study, we describe a new Neocalceostomoides species from the gills of Cathorops spixii using an integrative taxonomic approach that combines morphological and molecular evidence. Additionally, Calceostomella herzbergii Zambrano, Dezón & León, 2004 is redescribed and transferred to Neocalceostomatidae as Neocalceostomoides herzbergii n. comb. Furthermore, finding Neocalceostoma elongatum Tripathi, 1957 infecting Genidens barbus in southeastern Brazil is the first record of Neocalceostomatidae in Neotropical ariid hosts, expanding the family's known range. We propose the first molecular phylogeny for the Neocalceostomatidae based on partial 28S rDNA, 18S rDNA, ITS1, 5.8S rDNA, and ITS2 sequences. Our results recover Neocalceostomatidae as a nested lineage within Dactylogyridae and closely related to lineages parasitizing ariid catfishes. This contradicts previous hypotheses that the group is a derived lineage of Calceostomatinea or an independent Dactylogyridea lineage. Although our results indicate Neocalceostomatidae may represent a derived lineage of Dactylogyridae, the family is provisionally retained pending broader taxonomic sampling and additional molecular data.