Fundal variations in the eyes of the osteoglossomorph fishes

The appearance of the fundus of the eye varies among the families of osteoglossomorph teleosts. In this study, four different fundal patterns were observed: (i) an anteroposterior (or horizontal) embryonic fissure with a septal falciform process (family Osteoglossidae); (ii) an embryonic fissure from the optic disc nasoventrally with a falciform process (family Arapaimidae); (iii) an embryonic fissure nasoventrally from the optic disc without a falciform process (family Hiodontidae); and (iv) neither an embryonic fissure nor a falciform process (families Notopteridae and Mormyridae). The distribution of these various forms among the osteoglossomorph fishes is consistent with the recent cladogram for the Osteoglossomorpha [Lauder and Liem, 1983] which was based on many characters. The embryonic fissure in adult Amia calva was also examined. Its existence in adult Amia, in most Osteoglossomorpha, and in many non-euteleostean bony fishes suggests that its persistence in the adult stage is a primitive trait of bony fishes, and its absence in the Notopteroidei (with the exception of Hiodon) is a derived condition.