By serial histological sections, embryos at different development stages were sampled and fixed to investigate the relationship between the organogenesis of yolk sac, hepatopancreas and the yolk utilization during the embryonic development of swimming crab,
Portunus trituberculatus
. The results showed that: (1) the formation of yolk island and yolk sac were in gastrula stage and egg nauplius stage, respectively, while the yolk islands could be found in the yolk sac from egg gastrula to egg Zoea I stage. (2) From egg Zoea II stage, the yolk sac was divided into two parts because of further development of the midgut while the hepatopancreatic cells (columnar epithelium) were appearing in the inner of yolk sac membrane. This indicated the starting formation of hepatopancreas. (3) At egg Zoea III stage, the yolk sac had been developed into a pair of hepatopancreas while the yolk from different yolk islands were combined, then all yolk islands disappeared from this stage. Due to yolk utilization, many vacuoles could be found in the hepatopancreatic lumen. (4) When the embryo developed into pre-hatching stage, the yolk in the lumen of hepatopancreas had been nearly depleted while for newly-hatched Zoea I, the yolk had been completely utilized and hepatopancreas seemed to be a pair of saccate structure. These results indicated that both the yolk islands and hepatopancreatic cells play important roles for the disintegration and utilization of egg yolk from gastrula stage to pre-hatching stage in
P. trituberculatus.
