Whalefishes, bignoses and tapetails – these three groups of deep-sea fishes couldn’t look more different. The whalefishes (Cetomimidae) have whale-shaped bodies with disproportionately large mouths, tiny eyes, no scales and furrowed lateral lines – narrow organs on a fish’s flanks that allow it to sense water pressure.
The tapetails (Mirapinnidae) are very different – they also lack scales but they have no lateral lines. They have sharply angled mouths that give them a comical overbite and long tail streamers that extend to nine times the length of their bodies.
The bignoses (Megalommycteridae) are very different still – unlike the other two groups, they have scales, their mouths are small and their noses (as their name suggests) are very large.
Based on these distinct bodies, scientists have classified these fishes into three distinct families. Now, it seems they are wrong. Amazingly enough, the three groups are all just one single family – the tapetails are the larvae, the bignoses are the males and the whalefishes are the females. The entire classification scheme for these fishes needs to be reworked, as many distinct “species” are actually different sexes or life-stages of the same animal.