3.1 Compound eye morphology
The O. oratoria has a pair of oval compound eyes that are
symmetrically distributed on both sides of the head. The compound eye is
composed of multiple orthohexagnal ommatidia with similar area and the
width of each ommatidium is about 800 μm (Figure.2-H). Two rows of
mid-band ommatidia are present in the compound eye (Figure.2-G). Each
ommatidium is composed of cone cells that converge photon, pigment cells
that recognize color, and retinular cells that convert light signals
from the outside to the inside (Figure.2-A-J). Meanwhile, the retinular
cells were structurally like that of other crustaceans and contained 2
cell types. The surface of retinal cells is lined with numerous
horizontal microvilli, which are aggregated to form rhabdom arrays
(Figure.2-A-L). We captured the square and oval of rhabdom (Figure.2-E,
K, and J), and we speculate that they may be proximal and distal
rhabdom, respectively. Additionally, we also found that the microvilli
from different retinular cells are arranged in a cross-over pattern
(Figure.2-K, and J).