Comparative anatomy of the caudal skeleton of lantern fishes of the genus Triphoturus Fraser-Brunner, 1949 (Teleostei: Myctophidae)

The caudal skeleton provides important information for the study of the systematics and ecomorphology of teleostean fish. However, studies based on the analysis of osteological traits are scarce for fishes in the order Myctophiformes. This paper describes the anatomy of the caudal bones of 3 Triphoturus species: T. mexicanus (Gilbert, 1890), T. nigrescens (Brauer, 1904) and T. oculeum (Garman, 1899). A comparative analysis was performed on cleared and stained specimens to identify the differences and similarities of bony elements and the organization of the caudal skeleton among the selected species. Triphoturus mexicanus differs from T. oculeum in the presence of medial neural plates and a foramen in the parhypural, while T. nigrescens differs from their congeners in a higher number of hypurals (2 + 4 = 6) and the separation and number of cartilaginous elements. This osteological description of the caudal region allowed updates to the nomenclature of bony and cartilaginous elements in myctophids. Further, this study allows for the recognition of structural differences between T. mexicanus and T. oculeum, as well as the major morphological distinction between T. nigrescens and their sister species.