The Stylophthalmine trait is an adaptation present in the

larvae A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. T ...

of several different species of actinopterygian fish. It is characterised by the development of elliptically shaped eyes, which are situated at the apex of long periscopic stalks extending from the larva's head. Stylophthalmine can be used as a general term to describe such larvae.King, D. (2014), "Looking through the deep - The Stylophthalmines and their amazing eyestalks", Life Nature Magazine, Jun 14, pp.18-19. The trait has developed as a result of

convergent evolution Convergent evolution is the independent evolution of similar features in species of different periods or epochs in time. Convergent evolution creates analogous structures that have similar form or function but were not present in the last com ...

at least 4 times in different groups of fish; twice in the family Myctophidae (in species of '' Myctophum'' and '' Symbolophorus''), and also in the families

Stomiidae Stomiidae is a family of deep-sea ray-finned fish, including the barbeled dragonfishes. They are quite small, usually around 15 cm, up to 26 cm. These fish are apex predators and have enormous jaws filled with fang-like teeth. They are ...

(genus '' Idiacanthus''), and

Bathylagidae The deep-sea smelts are any members of the family Bathylagidae, a distinct group of marine smelts. Deep-sea smelts are marine fishes found in deep waters throughout the oceans, down to in depth. They are small fishes, growing up to long. They ...

(''

Bathylagus ''Bathylagus'' is a genus of deep-sea smelts, some species of which are noted for having stylophthalmine larvae. Species The seven recognized, extant species in this genus are: * '' Bathylagus andriashevi'' Kobyliansky, 1986 * '' Bathylagus an ...

''). The work of Weihhs and Moser (1981) showed that the eye's elliptical shape allows a stylophthalmine to dramatically enlarge its

field of view The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation. Humans a ...

through rotation on the stalk, giving a much larger effective pupil size. Three unrelated species with stylophthalmine larvae were once placed in the now discredited genus '' Stylophthalmus''.

References

{{Reflist Evolutionarily significant biological phenomena Ray-finned fish Fish anatomy