An ultrastructural study on the origin of glomerulocytes, a type of blood cell in a styelid ascidian, Polyandrocarpa misakiensis

The glomerulocyte is a type of blood cell in the compound ascidian, Polyandrocarpa misakiensis. It is a discoidal cell, measuring 12-13 μm in diameter and about 3 μm in thickness. The outer half of the cell is occupied by concentrically-arranged fibers, usually 0.2-0.3 μm thick; the nucleus and organelles are confined to the central cytoplasm. The ordinary epidermal cells are columnar and are characterized by an apical homogeneous cytoplasmic bulge, vesicular bodies in the cytoplasm, and juctions between them. Growing or immature glomerulocytes are found only in the epidermis. They have intracellular fibers and vesicular bodies, and there are juctions between them and epidermal cells. These facts strongly suggest the origin of the glomerulocyte from an epidermal cell. However, no definite statement can be made as yet because earliest stages of differentiation have not been observed. The glomerulocyte fully differentiated in the epidermis is apparently released into the hemocoel.