Morphology and Ultrastructure of the Compound Eye in the Mud Crab (Scylla serrata)

The morphology and fine structure of the compound eye in Scylla serrata was observed with electron microscopes (EM).Under the scanning EM,there was a thumb-shaped area with no ommatidia on the back of the compound eye.Under the transmission EM,ommatidia were hexagon,which are specific to Decapoda Brachyura;the sensitization system of an ommatidium included 11 retinular cells (RCs),of which four located at the distal part of the ommatidium;seven formed the proximal main part of the retina.Thus a "4+7"structure could be seen at the conjunction area,partly in overlap.These observations are in keeping with those reported for Portunus tritubereulatus and the larval of Macrobrachium rosenbergii,but different from those with the structure of "1+7" in Libinia and Eriocher sinensis.The difference may be related to the dependence of the species on the visual sense in their natural habitats.