Meeting Abstract
Myctophids, commonly referred to as lanternfishes, constitute the majority of all deep-sea biomass and are known for their ecological importance in the oceanic food web and as a major component in global oceanic carbon distribution. Recent molecular phylogenies suggest that myctophids are sister to acanthomorphs, a species-rich clade that has evolved the ability to protrude the upper jaw during feeding. Despite the documented significance and importance of myctophids, their cranial morphology is vastly understudied and little is known about how these fish feed. Because myctophids are considered to be the outgroup to Acanthomorpha, studying the cranial morphological characters may provide clues on the evolution of the premaxillary protrusion feeding mechanism in acanthomorphs. Here we document the cranial anatomy of Myctophum nitidulum, with a focus on the soft tissue linkages within the jaws and between the jaws and the rest of the cranium. M. nitidulum has a relatively large gape, averaging 50% of the overall head length. A rostral cartilage is present caudoventral to the ascending processes of the premaxillae, which are relatively small compared to the ascending processes found in acanthmorph species. The rostral cartilage in M. nitidulum is similar to the rostral cartilage that is common in acanthomorphs. A band of dense fibrous connective tissue tightly binds the premaxillae to the maxillae and to the rest of the head, which prevents the possibility of upper jaw protrusion. Understanding the various morphological characters of myctophid jaws not only facilitates development of hypotheses on the evolution of premaxillary protrusion in acanthomorphs, but also allows for inferences on the functional aspects of prey capture and processing in a family of fishes that are a vital component in the circumglobal oceanic food web.
