The ultrastructural identity of some cells in Sphaerolaimus gracilis de Man, 1876

The fine structure of fibroblasts, lymphocytes, neurosecretory cells, stem cells, and steroidogenic cells in the nematode Sphaerolaimus gracilis was studied by transmission electron microscopy. Fibroblasts, lymphocytes, and stem cells were found in the lateral position at the level of the renette pore (ventral pore). Fibroblasts were characterized by long cellular processes. The cytoplasm consisted of a network of irregularly arranged microscopic filaments. The nucleus was large, triangular, rectangular, or oval. Occasionally, small, oval, or basket-shaped mitochondria and some cisternae of rough endoplasmic reticulum were observed in the periphery of the cell. Lymphocytes were round and had a large round nucleus encircled by a thin cytoplasmic rim. Indistinct cisternae of rough endoplasmic reticulum, an oval mitochondrion, and several ribosomes were observed in the cytoplasm. A large rectangular stem cell dorsally abutted lymphocytes on both sides of the esophagus. The cytoplasm of stem cells had tiny cisternae of the rough endoplasmic reticulum and small vesicles in the periphery of the cell. The nucleus was large and rectangular, and the nucleolus was characterized by a granular structure. Steroidogenic cells were embedded into the lateral epidermal cord of the midbody. The cell was characterized by a large nucleus, a voluminous vacuole, a mitochondrion of tubules, and several vesicles in the cytoplasm. Neurosecretory cells and interneurons were found in the lateral midbody close to the steroidogenic cells. The present study aimed to characterize the ultrastructure of the cells of Shaerolaimus gracilis with their close structural resemblance to fibroblasts, lymphocytes, stem cells, steroidogenic cells, and neurosecretory cells in other animals and evaluate their possible function when considering their morphology.