NEW SPECIES OF AXINE ABILDGAARD, 1794 (MONOGENOIDEA: AXINIDAE) INFECTING GILL LAMELLAE OF ATLANTIC FLYINGFISH, CHEILOPOGON MELANURUS (VALENCIENNES) (EXOCOETIDAE) IN THE WESTERN ATLANTIC OCEAN WITH PHYLOGENETIC ANALYSIS AND COMMENTS ON THE FEMALE GENITALIA OF AXINE SPP.

We collected specimens of Axine trickyvagina Brule and Bullard n. sp. (Monogenoidea: Axinidae) from the gill lamellae of Atlantic flyingfish, Cheilopogon melanurus (Valenciennes) (Exocoetidae) in the north-central Gulf of America. Specimens of the new species were heat-killed and formalin-fixed for morphology, and others were preserved in 95% EtOH for DNA extraction and sequencing of the 28S gene and ITS1 region. The new species differs from all congeners by the combination of having a long haptor (∼40-50% of the total body length), a male copulatory organ with 10-15 spines, and a genital atrium having bilateral spinous patches each with 18-25 spines. Our study of specimens of the new species, type and voucher specimens representing 8 congeners, and all published accounts of all congeners revealed that the terminal female genitalia of Axine spp. comprises 2 ducts (a multi-chambered vagina that lacks a sclerite plus an accessory duct with a sclerotized nozzle comprising its opening) that open into a common female genital atrium. Descriptions of Axine spp. published from 1794 through 2023 failed to recognize the vaginal duct and accessory duct as distinct components and unanimously misinterpreted the accessory duct's sclerotized nozzle as a "vaginal spine." The phylogenetic analysis inferred from 28S rDNA sequences placed our sequence in a clade of other Mazocraeidea spp. and sister to a nonugen sequence ascribed to Axine japonicaPrice, 1946 (GenBank LC799038). We recovered Axinidae as sister to Heteromicrocotylidae, Heteraxinidae, and Microcotylidae. The present study is the first published description of an axinid from a flyingfish in the western Atlantic Ocean.