The structure of photoreceptors (PR) and the arrangement of neurons in the retina of
red-tail shark were investigated using light and electron microscopy. The PR showed
a mosaic arrangement and included double cones, single cones (SC), and single rods.
Most cones occur as SC. The ratio between the number of cones and rods was
3:1.39 (±0.29). The rods were tall that reached the pigmented epithelium. The outer
plexiform layer (OPL) showed a complex synaptic connection between the horizontal
and photoreceptor terminals that were surrounded by Müller cell processes. Electron
microscopy showed that the OPL possessed both cone pedicles and rod spherules.
Each rod spherule consisted of a single synaptic ribbon within the invaginating terminal endings of the horizontal cell (hc) processes. In contrast, the cone pedicles possessed many synaptic ribbons within their junctional complexes. The inner nuclear
layer consisted of bipolar, amacrine, Müller cells, and hc. Müller cells possessed intermediate filaments and cell processes that can reach the outer limiting membrane and
form connections with each other by desmosomes. The ganglion cells were large multipolar cells with a spherical nucleus and Nissl’ bodies in their cytoplasm. The presence of different types of cones arranged in a mosaic pattern in the retina of this
species favors the spatial resolution of visual objects.