Occurence of high crystalline cellulose in the most primitive tunicate, appendicularian

Using electron diffraction analysis, highly crystalline cellulose Iβ was found in the house (a special structure in which the tunicate lives) of an appendicularian, Oikopleura rufescens. The cellulose microfibrils of 20 nm in width were observed in a random array or highly organized with 2 to 10rectangular spacings in the house. The bundled cellulose microfibrils formed in the inlet filters, which are highly ordered meshwork structure. This provides first account for the existence of cellulose in the house of the appendicularian. The evidence shows that the house and tunic are homologous tissue among the tunicates, and that the common ancestor of the tunicates (ascidians, thaliaceans, and appendicularians) had already possessed the ability of the cellulose biosynthesis. This investigation will offer a key to understanding whether the cellulose synthetic ability is universal or not in the tunicates, and how the cellulose biosynthetic ability is transmitted into the tunicates.