Various crab stages beginning with the invasive to adult stages of male and female of Pinnotheres placunae infesting the window-pane oyster Placenta placenta of the Kakinada Bay have been described for the first time. The stage-wise and sex-wise frequency occurrence of P. placunae is given. The growth rate of the crab from the invasive to the mature stage has been correlated with the growth rate of the oyster. The index of condition of the infested versus non infested oysters showed significant difference. Damages to the gills and soft parts of the host were noticed. The infested oysters were mostly males. The oysters were hermaphroditic in most of the cases of multiple infestations.