AbstractThe genealogy of B‐cells in the hepatopancreas of decapod crustaceans is still a matter of intense debate. According to widely accepted two‐cell‐line concepts, B‐cells are supposed to originate either from secretory F‐cells or absorptive R‐cells. These concepts are based on the putative lack of B‐cells in the differentiation zone of the hepatopancreas tubules. In the giant tiger prawnPenaeus monodonI could clearly identify differentiating B‐cells in that zone by using an ultrastructural distinguishing mark, the apical complex, that is much more sensitive than markers used before. Tracking of this feature from mature B‐cells through the differentiation zone up to the embryonic E‐cells revealed that B‐cells directly originate from E‐cells. The recognition of B‐cells as a separate cell line calls for a new functional interpretation. Ultrastructural and histochemical data suggest a degrading function. B‐cells may clear the hepatopancreas tubules from remnants of digestion in the time span between nutrient absorption and secreti