Fine structures of the mantle tissue in the pinkish-brown salp Pegea confoederata (Tunicata: Thaliacea)

Abstract

Pegea confoederata is a salp with a pinkish-brown body. The color was retained in the mantle tissue, while the tunic was transparent. We examined the fine structures of the mantle tissue to clarify the cytological basis of the body coloration. Apical cytoplasmic bulges of the epidermal cells were associated with dense tunic fibers, suggesting an involvement in the secretion of the tunic. Light microscopy analysis of the mantle revealed pigment cells that are dendroid-shaped hemocytes filled with brown granules. Five types of hemocytes were recognized in the hemocoel, based on their ultrastructure, and the pigment cells in the present species were hemocytes classified as ‘storage cell’. Additionally, some hemocytes were seen to have migrated into the tunic through the epidermis, and were supposed to be presumptive tunic cells.