Budding and regeneration potential of a calyx of a freshwater Kamptozoan, Urnatella gracilis.

There are only two freshwater Kamptozoans worldwide: Urnatella gracilis Leidy, 1851 and Loxosomatoides sirindhornae Wood, 2005. U. gracilis is present in Japan and is expanding its distribution, especially in Lake Hachiro. We investigated the budding and regeneration potential of a calyx of U. gracilis to clarify the mechanisms underlying its ability of regeneration. Our experiments revealed that the formation of a new calyx at the most apical position and strong adaptation to freshwater in pH 7.0. Budding successfully occurred in water with 0% salinity, however, in water with 0.15%-0.3% salinity budding was occurred in low level. These features may be very useful for propagation at Lake Hachiro in which it has to be expected that no sexual reproduction is observed because of low temperatures below 28°C. Now as Lake Hachiro has water with no salinity and almost pH 7.0, Lake Hachiro is a good place to live for U. gracilis.

The postbranchial digestive tract of the ascidian, Polyandrocarpa misakiensis (Tunicata: Ascidiacea). 2. Stomach.

The organization of the stomach in the compound styelid ascidian, Polyandrocarpa misakiensis, is described, and the morphology and cell types of the stomach is discussed from the phylogenetic viewpoint. The stomach is a sac-like organ whose wall is formed into longitudinal folds. The stomach consists of external and internal epithelium. The internal epithelium is simple columnar, except for the bottom of the folds. There are five cell types: absorptive cells, zymogenic cells, endocrine cells, ciliated mucous cells, and undifferentiated cells. The absorptive cells have numerous microvilli. The apical region of these cells is occupied by coated vesicles. The zymogenic cells have a conical outline and a few microvilli on their apical surfaces. There are secretory granules in the apical region of zymogenic cells. The endocrine cells have low cell height and electron-dense granules around the nucleus. Endocrine cells have one or two cilia and a few microvilli on the apical surfaces. The basolateral part of these cells often bulges into the adjoining cells. Immunoelectron microscopy revealed that some endocrine cells have serotonin-like immunoreactivity. The ciliated mucous cells are restricted to a single ventral groove. They have numerous microvilli and a few cilia on their apical surfaces. Moderately electron-dense granules are accumulated in the apical part of the ciliated mucous cells. Undifferentiated cells, filled with free ribosomes, form a pseudostratified epithelium in the base of each fold. The nucleus of undifferentiated cells has a prominent nucleolus. The pseudostratified epithelium of the pyloric caecum consists of electron-dense and electron-light cells.

Tunic phagocytes are involved in allorejection reaction in the colonial tunicate Aplidium yamazii (Polyclinidae, Ascidiacea).

The colonial ascidian Aplidium yamazii exhibited an allorejection reaction when two allogeneic colonies were brought into contact at their growing edges or at artificial cut surfaces. This species has no vascular network in the tunic, unlike the botryllid ascidians, which have a vascular network throughout the colony's common tunic. In the allorejection reaction induced by contact at the growing edges, some small, hard-packed tunic masses were formed at the contact points. Histological and electron microscopic investigation of these tunic masses revealed that they contained aggregates of tunic cells, with tunic phagocytes being the major cell type present. Some of the tunic phagocytes in these tunic masses appeared to be disintegrating. When allogeneic colonies were placed in contact at their artificial cut surfaces, the colonies partially fused, then separated. In this allorejection reaction, some loosely packed tunic masses remained in the gap between the two withdrawn colonies. These results strongly suggest that the tunic phagocytes are likely to be the major effector cells in the allorejection reaction. We also propose that the tunic phagocytes are not only the effector cells in the allorejection reaction but also bear the sites of allorecognition.

Study of color variation in the solitary ascidian Halocynthia roretzi, collected in the Inland Sea of Japan.

In the vicinity of Yashiro Island in the Inland Sea of Japan, the solitary ascidian (tunicate) Halocynthia roretzi with tunics of various colors were collected. Samples of these animals were sorted into three groups on the basis of visual observation of tunic color. The red group includes animals with dark-red, light-red, or orange tunics. The pink group includes animals with tunic colors ranging between red and white. The white group includes only animals with completely white tunics. Animals in the white group lacked color internally, with the exception of the hepatopancreas and the gonads in breeding season; the epidermis and gill basket were white. In contrast, animals of both the red group and the pink group were colored internally, with red-orange epidermis and yellow gill basket. Alloreactivity was tested by mixed-hemocyte incubation between different animals belonging to the same color group and between animals belonging to different color groups. Alloreactivity between animals of the white group was 56.3%, between animals of the pink group was 60.0%, and between animals of the red group was 69.3%. The relatively high frequency of compatible combinations among the white animals is discussed.