Abstract
All tunicates produce a cellulosic extracellular matrix external to the epidermis; this is the most remarkable character of the subphylum (Tunicata = Urochordata). In Ascidiacea and Thaliacea, two of the three classes of Tunicata, cellulose is the main component of the tunic matrix that covers the whole body. In Appendicularia, however, the animals do not possess a tunic, and instead secrete a feeding apparatus called a "house" that is composed of cellulose. In the appendicularian Oikopleura dioica, we found a unique intracellular matrix in the apical cytoplasm of the adult tail epidermis that appears to form a tough shell supporting the tail. Although some experimental data suggest that this matrix may contain cellulose, the composition is still unknown. The significance of the tunicate capacity for cellulose synthesis is briefly discussed.