Coherence in nervous system design: the visual system of Pantodon buchholzi

One of the mc,re unusual visual systems of the Actinopterygii is that of Pa ntodon buchholzi (Osteoglossomorpha: Osteoglossidae). Its adaptations assoc iate neuroanatom) at different levels of the visual system with ecological and behavioural correlates and demonstrate that the visual system of this f ish has adapted for simultaneous vision in air and water. The visual field is divided into three distinct areas: for viewing into the water column, in to air, and for viewing the aquatic reflection from the underside of the wa ter surface. Cone diameters in different retinal areas correlate with the d iffering physical constraints in the respective visual field. Retinal diffe rentiation between the aquatic and aerial views is paralleled at different levels of the central nervous system. A diencephalic nucleus receives both direct and indirect (tectal) afferent input from only the aerial visual sys tem and a specific type of cell in the optic tectum is preferentially distr ibuted in the tectum processing aerial inputs. Distinctions within a single sensory system suggest that some behaviours may be organized according to visual field. For Pantodon, feeding is initialed,) stimuli seen by the vent ral hemiretina so the anatomical specializations may well play an important role as elements in a feeding circuit.