[2][3] The first specimen of M. johnsonii was discovered by the English naturalist James Yates Johnson near Madeira, an archipelago off the coast of northwestern Africa, on December 24, 1863.

Early hypotheses about anglerfish behavior posited that their illicium and esca, the extended dorsal fin spine and bulbous apparatus that protrude from the snout, are used for luring prey.

[5] Until the 1920s, male specimens without a luring apparatus had been thought to be distinct, and were placed in separate taxonomic categories from their female counterparts.

[9] Female humpback anglerfish have short, globular bodies, large heads with a widened mouth that is nearly vertical, and long pointed teeth capable of eating prey larger than themselves.

[9] Like all other anglerfish, females have a short dorsal fin spine (illicium) with a bulbous luring apparatus (esca) on the snout.

[5] Female M. johnsonii have small, subcutaneous eyes that may suggest their lack of dependency on visual sight for feeding and reproduction.

[9] Humpback anglerfish exhibit extreme sexual dimorphism, with larger sized females and dwarfed males.

[5] Males lack a luring apparatus, but have large eyes and nostrils which may be helpful for locating far dispersed mates.

[5] M. johnsonii females have large mouths filled with sharp teeth and huge stomachs that make them capable of eating nearly everything they encounter.

Researchers found that M. johnsonii is able to regulate its aerobic metabolism by adjusting its oxygen consumption, allowing it to live in hypoxic or anaerobic conditions for long periods of time.

[13][14] It was originally thought that E. escacola was an obligate symbiont of its host because its genome was reduced about 50% compared to an average free-living bacterium.

[6] Males have highly developed sensory organs that allow them to trace the scent of a female as it is minimally disrupted in the still waters of the deep sea.

However, individuals may be collected as bycatch with trawling, and as commercial fisheries shift more toward deep sea resources, the species may become more affected by this catch.

[12] M. johnsonii was filmed in 2014 off of the coast of California by the Monterey Bay Aquarium Research Institute using their remotely operated submersible Doc Ricketts.