Histomorphology and ultrastructure of the hepatopancreas of a brachyuran crab, Varuna litterata (Fabricius, 1798)

The present study aims to describe the histomorphology and ultrastructure of the hepatopancreas of a brachyuran crab, Varuna litterata using light and transmission electron microscopy. The hepatopancreas is an orange-yellow-coloured bilobed organ that comprises numerous blind-ended tubules. Each tubule is divided into proximal, mid, and distal regions and lined by pseudostratified epithelium with five cell types (E-, F-, R-, B-, M-cells). Each cell has distinct cytomorphological features and their relative percentages can vary along the length of the tubules. E-cells are embryonic cells and confined to the extreme distal end. It has a high nucleus-to-cytoplasm ratio and is involved in mitotic activity. M-cells are infrequently scattered throughout the length of the tubule without any brush border and play an important role in nutrient and endocrine regulation. R-cells exhibit a distinct polar organization of the cell organelles into apical, medial, and basal areas and are responsible for nutrient absorption, storage, and detoxification processes. F-cells contain abundant rER that gives fibrillar appearances to the cytoplasm and are involved in the synthesis of digestive enzymes. B-cells have an apical endocytotic complex in the early stage and a large central vacuole in the final stage of maturation. Mature B-cells are eliminated into the tubular lumen by holocrine secretion. These are considered for intracellular digestion and excretory functions. These findings provide the basic information regarding the identification, characterization, and functions of the hepatopancreatic cell types of V. litterata that might be useful in further nutritional research as well as in histopathological and biomarker studies.