Cellular components and tunic architecture of the solitary ascidian Styela canopus (Stolidobranchiata, Styelidae)

: Cell distribution and tunic morphology in the ascidian Styela canopus were examined by electron microscopy. The observations showed that the outer covering is composed of a thin sinuous cuticle with several protrusions and a deep layer of ground substance. The fibrous component and its arrangement in the tunic were demonstrated: elementary fibrils exhibit a 'microtubular' structure and an elliptical cross-sectional shape. Four types of cells were described: clear vesicular tunic granulocytes, tunic microgranulocytes, unilocular tunic granulocytes, and globular tunic granulocytes. Morphofunctional aspects of the tunic tissue and certain phylogenetic relationships are discussed.