Using morphological and mitogenomic sequence data, Johnson et al. (2009) have shown that fishes formerly placed in the family Megalomycteridae (bignose fishes) are actually the males of Cetomimidae (whalefishes). These findings were very surprising since there is great sexual dimorphism associated with distinctly different life styles. Adult females have huge mouths suitable for the captureof large prey, while adult males do not feed at all. They losetheir stomach and esophagus, instead relying on a massiveliver for nutritional support throughout adult life.
Until recently, these elusive deep sea fishes where only known from adult female specimens. In 2009, Johnson et al. (2009) showed that both males and juveniles of this group had been classified in their own, separate families: males as Megalomycteridae (largenose fishes) and juveniles as Mirapinnidae (tapetails). Johnson et al. (2009) point out that the whalefishes' combination of extraordinary ontogenetic transformations with extreme sexual dimorphism is unparalleled within vertebrates.
Using morphological and mitogenomic sequence data, Johnson et al. (2009) have shown that fishes formerly placed in the family Mirapinnidae (tapetails) are actually the larvae of Cetomimidae (whalefishes). These findings were very surprising since tapetails and whalefishes share very few morphological or ecological similarities. While the pelagic larvae live in the nutrient-rich habitat of the sunlit zone (above 200 m depth), adults are found only in the nutrient-poor waters of the bathypelagic realm (1000–4000 m). Metamorphosis from larva to adult involves dramatic changes in the skeleton, especiallythe head, which are associated with distinctly different feeding mechanisms.
