Background: Few studies concerning Biomphalaria alexandrina (B. alexandrina) snail hemocytes’subpopulations, and their relation to the compatibility with Schistosoma mansoni (S. mansoni)’ miracidiawere performed. Manipulation of parasite development inside these snails could be applied as a controlmeasure against schistosomiasis.Objectives: Knowing that the snail hemocytes temporarily bind to the parasites, allowing the developmentof cercariae that are infective to the definitive host. This study aimed at studying the morphology andkinetics of diverse hemocytes of susceptible and resistant B. alexandrina and their participation in thesnail early immune response after challenge by S. mansoni.Material and Methods: Giemsa stained hemocytes were characterized using light microscopy. Total anddifferential hemocyte counts (THC and DHC) were calculated in the hemolymph of two groups composedof 60 susceptible and 60 resistant snails. Each group was further subdivided as 12 control pre-exposuresnails (PE) and 48 post-exposure snails (PO) to S. mansoni at different time points (6 h, 1, 3 and 7 days).THC and DHC counts were recorded by a snail hemogram.Results: Results revealed that granulocytes constituted the most common population all through theexperiment with the large dense-granulated granulocytes subpopulation being the largest-sized cellsdetected. The highly reactive subpopulations that increased in number upon exposure to S. mansoni werethe few-granulated and the large-granulated granulocytes, suggesting their possible participation in earlyparasite destruction.Conclusion: The resulting hemograms helped determine the participation of hemocyte populations andsubpopulations in the defense against S. mansoni, aiding in understanding snail compatibility patterns.Further studies to propagate transgenic B. alexandrina snails abundant in large granular granulocytesutilizing (gene editing) CRISPR-Cas9 technique are recommended. This would be required to spreadschistosome resistance traits in snail populations, thus, contributing to reduced schistosomiasistransmission in the long run.