First morphological description of hemocyte subtypes in the freshwater bivalve Corbicula largillierti.

The genus Corbicula is a relevant bioindicator of environmental contamination. However, reports on hemocyte subpopulations in Corbicula are scarce, and to date, studies focusing on the immunological system of Corbicula largillierti have not been found. The objective of the present study is to provide a morphological characterization of hemocyte subpopulations in the freshwater bivalve C. largillierti. Adult C. largillieti individuals were collected, acclimated under controlled conditions for 30 days, and subsequently decontaminated for 48 h in dechlorinated tap water and autoclaved. Following this, hemolymph (He) and pallial fluid (Lp) were extracted by puncture. A pool of four individuals was used per experiment. Cell counts were performed using a Neubauer chamber, and cells were stained with May-Grünwald-Giemsa. Differential counting and morphological characterization were performed using light microscopy. Six different hemocyte subtypes were found; the most abundant in both compartments were small hyalinocytes (63.09 % ± 11,38 in He and 58.64 % ± 14,61 in Lp). We also report the presence of large hyalonocytes, eosinophilic and basophilic granulocytes, already described in other bivalve species of the same family, and two cell subtypes not reported in other bivalve species of the Corbiculidae family: a plasmacyte-like cell with clear cytoplasmic inclusions and an eccentrically located nucleus, and another large cell that we have termed a giant granular cell (43.49 μm ± 11.11 in He and 52.07 μm ± 16.97 in Lp). Our preliminary results constitute the first report on hemocyte subtypes in C. largillierti.