Morphological characteristics of visual cells in the endemic Korean loach Kichulchoia multifasciata (Pisces; Cobitidae) by microscopy.

The visual cell of the retina in the Korean loach Kichulchoia multifasciata, a bottom-dwelling freshwater loach in shallow water, contains double cones and large rods. With light microscopy, the cones form a row mosaic pattern in which the partners of double cones are linearly oriented with a large rod. In a double cone or twin cone, the two members are unequal such that one cone may be longer than the other. An anatomical unit is apparent which consists of 5 rod cells and 15 double cone cells per 20 × 20 μm area. We found that the cone cells of outer segments are linked to the inner segment by so-called "calyceal process" using a scanning electron microscopy, unlike rod cells. In the transmission electron microscopy, the outer membrane shows piles of membrane discs surrounded by double membranes.