In vitro nodule formation in the ridgeback prawn, Sicyonia ingentis, and the American lobster, Homarus americanus

Bacteria injected into the hemolymph of crustaceans are rapidly cleared from circulation; many accumulate in the gills, even though this organ does not contain fixed phagocytic cells. In this study, hemolymph from a shrimp or a lobster was mixed in a culture medium with or without bacteria. In all cases, hemocytes rapidly aggregated to form nodules. As nodules increased in size, the number of free hemocytes, nodules, and bacteria (if present) decreased. Nodule formation was inhibited by the addition of the peptide RGD (Arg-Gly-Asp). The morphology of the nodules formed in the presence and absence of bacteria was examined using light and electron microscopy. Within 10 min, nodules were larger than the small blood spaces of the gills, suggesting that in vivo clearance is the result of physical entrapment of nodules and foreign material in the narrow vessels of the gills. This method of removing foreign material from circulation is discussed in relation to other clearing mechanisms in crustaceans.