Lanternfishes (Myctophidae) are a highly diverse and globally-important family of fishes, which form a ubiquitous part of the deep-pelagic micronekton. The majority of lanternfish species conduct diel vertical migrations (DVMs) from the mesopelagic (200 - 1000 m) to the epipelagic (0 - 200 m) where they feed at night. As voracious zooplanktivores and an important food source for commercially-important fishes, seabirds, and deep-living predators, myctophids play a key role in the biological pump and are an important intermediate trophic group, linking coastal, upper-ocean and deep-ocean ecosystems. Nonetheless, relatively little is known about the variability of myctophid biodiversity, assemblage structure and species distribution patterns, or of their DVM behaviours over spatial and temporal scales. In this study, we present a synthesis of recent research findings examining vertical and horizontal distribution patterns in a high-diversity myctophid assemblage in the Gulf of Mexico, and their variability both through time and in relation to mesoscale oceanic processes. The analyses were conducted using depth-stratified data (spanning 0 - 1500 m), collected between 2011 and 2017 across a 200 x 700 km survey area. Analyses indicate that the lanternfish assemblage in the Gulf of Mexico is weakly structured, and shows limited coherence at the measured scales. However, individual species show stronger responses to mesoscale environmental conditions, which are evidenced primarily by changes in their vertical migratory behaviours. These findings suggest that the overall assemblage is comprised of a highly-dispersed, well-mixed suite of individual populations and life-stages, which respond independently to environmental cues. We discuss the implications of these findings for ecosystem structuring and carbon transfer between the surface and deep oceans.