The photoreceptors of Muraena helena and Ariosoma balearicum - a comparison of multiple bank retinae in anguilliform eels (Teleostei)

The retinas of two anguilliform teleosts, the moray eel Muraena helena and the conger eel Ariosoma balearicum have been studied by electron microscopy . In both species duplex retinas composed of single cones and multiple rod banks are found. M. helena has large cones, two rod layers and the rod/cone ratio is 15:1 in the ventrotemporal retina. A. balearicum possesses very s mall cones, five rod layers and a rod/cone ratio of 50.1. The photoreceptor s of all the rod layers show ultrastructural features indicative of visual functioning. A comparison of different Anguilliformes reveals that multiple bank retinae are a basic feature of this teleost group. The different numb ers of rod banks and rad-cone ratios can be inferred from the specific phot ic habitats of these species.