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).