. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ROUNDING OF ASCIDIAN TUNIC SLICES 33 IDJ IB. Figure 5. Microfilaments in the tunic specimens stained with phalloidin-FITC. In a newly sliced tunic, elongated tunic cells extending tilopodia form a cellular network (A). The cellular network has disappeared in the tunic slices incubated in Ca2*-Mg2*-free-ASW (B), or incubated in cytochalasin B-ASW (10 Mg/ml) (C). Cryostat sections of colony pieces (D) and rounding tunic balls (E). showing cortical area ot the specimens. Arrow indicates tunic cuticle. Magnifications are the sam
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. ROUNDING OF ASCIDIAN TUNIC SLICES 33 IDJ IB. Figure 5. Microfilaments in the tunic specimens stained with phalloidin-FITC. In a newly sliced tunic, elongated tunic cells extending tilopodia form a cellular network (A). The cellular network has disappeared in the tunic slices incubated in Ca2*-Mg2*-free-ASW (B), or incubated in cytochalasin B-ASW (10 Mg/ml) (C). Cryostat sections of colony pieces (D) and rounding tunic balls (E). showing cortical area ot the specimens. Arrow indicates tunic cuticle. Magnifications are the same for all parts of this figure. Scale bar = 50 jim. The tunic cells forming the network have been de- scribed as "elongated tunic cells" (Hirose et 1994b) and probably correspond to the "myocytes" described in Diploxoma species (Mackie and Singla. 1987). The myocytes also form a network in the tunic, and the net of myocytes itself is supposed to conduct impulses that trigger its contraction, according to electrophysiological studies (Mackie and Singla, 1987). Elongated forms of tunic cells were also reported in Leptodinides echinatits (Hirose. 1992), although it is uncertain whether they form a network. On the other hand, similar types of tunic cells or tunic cell network have not been described in other colonial ascidians that have colonial vascular networks in the tunic, such as Clavelina miniata (Aoki et al., 1989), Perophora viridis (Deck et 1966), and Botryllus and Botrylloides species (Zaniolo, 1981; Hi- rose et ul., 1991). Although the epidermal cells of the vascular network show contractility (Mukai et 1978) and impulse conductivity (Mackie and Singla, 1983), the tunic cell network may be uniquely developed in some colonial species that lack a colonial vascular net- work. The fine-structure study revealed that the tunic cuticle, a thin, electron-dense layer, had regenerated in the rounding tunic ball and covered the entire surface. I
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