Mukai Hideo, Sugimoto Keiji, Taneda Yasuho
Department of Biology, Faculty of Education, Gunma University, Maebashi 371, Japan.
Department of Anatomy, Nippon Medical School, Sendagi, Bunkyo-ku, Tokyo 113, Japan.
J Morphol. 1978 Jul;157(1):49-77. doi: 10.1002/jmor.1051570105.
The circulatory systems of four polystyelids, Botryllus schlosseri, B. primigenus, Botrylloides violaceus and Symplegma reptans, were compared. The palleal buds are connected to the parent zooid by a peduncle and to the colonial vascular system by connecting vessels. The peduncle of S. reptans disappears at an earlier stage of bud development than in B. primigenus; it survives the dissolution of the parent zooid in B. schlosseri and B. violaceus. The connecting vessel is formed by anastomosis between an epidermal outgrowth from the bud and a neighboring colonial vessel, and is characterized by the presence of a sphincter. The number of connecting vessels formed in a palleal bud is three in S. reptans, two in B. primigenus and one each in B. schlosseri and B. violaceus. In each species, the larva has eight rudiments of ampullae. In B. primigenus, the original ampullae degenerate soon after metamorphosis and new ampullae extend from the ventral epidermis of the oozooid. In the other species, the colonial vascular system is derived from the original ampullae. The whole colonial vascular system contracts and expands periodically, with regionally different phases. During each expansion cycle, the sphincter contracts once in B. primigenus and twice in S. reptans. The correlation may be due to blood pressure and the propagation of excitation through the colonial vascular system.
对四种多柄海鞘（Botryllus schlosseri、B. primigenus、Botrylloides violaceus和Symplegma reptans）的循环系统进行了比较。芽体通过柄与亲代个体相连，并通过连接血管与群体血管系统相连。Symplegma reptans的柄在芽体发育的早期阶段就消失了，比B. primigenus消失得更早；在Botryllus schlosseri和Botrylloides violaceus中，它在亲代个体溶解后仍然存在。连接血管由芽体的表皮突出与相邻的群体血管吻合形成，其特征是存在一个括约肌。Symplegma reptans的芽体中形成的连接血管数量为三条，B. primigenus为两条，Botryllus schlosseri和Botrylloides violaceus各为一条。在每个物种中，幼虫都有八个壶腹原基。在B. primigenus中，原始壶腹在变态后不久就退化，新的壶腹从卵囊的腹侧表皮延伸出来。在其他物种中，群体血管系统源自原始壶腹。整个群体血管系统会周期性地收缩和扩张，各区域的阶段不同。在每个扩张周期中，B. primigenus的括约肌收缩一次，Symplegma reptans的收缩两次。这种相关性可能是由于血压以及兴奋在群体血管系统中的传播所致。
