Morphology and differentiation of the coelomocytes of the free-living stages of Nippostrongylus brasiliensis.

With the use of observations on living and fixed and stained larvae of Nippostrongylus brasiliensis reared in charcoal-feces cultures, an integrated view is presented on the morphology and differentiation of the coelomocytes present in the body cavity of the 2 rhabditiform stages and the exsheathed third stage. Four coelomocytes are present in the newly hatched larva arranged linearly from the base of the esophagus to the genital primordium. They lie subventrally, the anterior 2 on the right side of the ventral nerve cord, the posterior 2 on the left side. Data on the growth of these cells and analysis of their fixed site location in the coelom are presented. The coelomocytes are firmly attached to the inner surface of the body wall by filopodia. However, aberrantly positioned coelomocytes suggest the possibility that detachment and migration may occur. A few minute cytoplasmic inclusions are present in the coelomocytes in living newly hatched larvae and may reach approximately 100 or more in each coelomocyte in the third stage. These inclusions exhibit 2 phases of a pigmentation process. They are colorless in the rhabditiform stages, but simultaneous with the initiation of the second molt to form the infective larva, the inclusions rapidly turn a pink to rose hue. A variety of previous experimental data strongly support the interpretation that the pigment represents an extraordinary concentration of vitamin B12 in the coelomocytes obtained by larval feeding on bacterial B12 synthesizers present in the charcoal-feces cultures.