The Viriform Cell Of Halocynthia Roretzi: Fine Structure, Distribution, And Appearance

The viriform cell (VC) in the tunic of Halocynthia roretzi is rod shaped (about 15x5 mum) and is characterized by intracellular eosinophilic and electron-dense granules (about 1-2 mum in diameter). The VC is confirmed to be a native tunic cell by the DNA fingerprint method. Light and electron microscopic observations and immunohistochemical findings demonstrated that VCs appeared in the tunic and hemocoel of about 3-month-old specimens but were not seen in younger juvenile specimens (2 weeks after metamorphosis). There were more VCs in the tunic matrix of 1-year-old specimens than in 3-month-old specimens. It seems that the cells migrated from the hemocoel through the epidermis. In mature specimens, the density of VCs was very high not only in the inner tunic matrix but also in the tunic of growing attachment villi. When the villi became brown, broken VCs were observed at the area just under the cuticle, where the subcuticle forms later. VCs also crowded at the repairing surface of the tunic after artificial injury. These findings suggest that VCs may play roles in subcuticle formation and wound healing.