The known mature male individuals are 6.2–7.3 mm, smaller than any other mature fish and vertebrate; the females, however, reach a significantly larger size of up to 50.5 mm. (However, numerous fish species have both sexes reaching maturity below 20 mm.)
Like other anglerfishes, Photocorynus spiniceps lures its prey using a bioluminescent spinal extension, and swallows the prey whole with the help of a distending jaw and a similarly distending stomach. Its prey can sometimes be as big as their own bodies. The male spends its life fused to its much larger female counterpart therefore effectively turning her into an hermaphrodite. While the female takes care of swimming and eating, the male, with a large proportion of its body consisting of testes, is charged with the task of aiding reproduction.