Zimmer Russel L, Woollacott Robert M
Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-0371.
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138.
J Morphol. 1989 Feb;199(2):125-150. doi: 10.1002/jmor.1051990202.
The larva of the ascophoran cheilstome Watersipora arcuata is described on the basis of serial 1-μ sections, light microscopy of whole mounts, and scanning electron microscopy. Using lightly osmicated specimens, it was possible to map almost every cell on the larval surface. Limited observations on hatching and larval behavior are provided in conjunction with the anatomical description. Tissues of the larva are partitioned between those that function exclusively during the larval period and are degraded at metamorphosis as transitory tissues and those that will have postmetamorphic fates in formation of the ancestrula. Significantly, W. arcuata has two possible anlagen for the ancestrular polypide, the infracoronal cells in the oral hemisphere and the epidermal blastemal cells in the aboral hemisphere, rather than only one or the other of these as reported in other species. Also detailed are the supracoronal flange and groove, which are unique to this genus and are involved in the transmission of mycoplasma-like organisms between successive generations of adults; two pairs of complex pigment cup ocelli; multiple intercoronal cells that are presumed to have varied sensory and mechanical functions; and the sensory, adhesive, and locomotory components of the pyriform organ. The larval anatomy of W. arcuata is compared with that of the larvae of the ctenostomes Alcyonidium gelatinosum (coronate), Bowerbankia imbricata (coronate), B. gracilis (coronate), and Flustrellidra hispida (shelled lecithotrophic) and of the cheilostomes Bugula neritina (coronate), Electra pilosa (cyphonautes), and Membranipora membranacea (cyphonautes). This study is the first detailed analysis of the larval structure of any ascophoran bryozoan and provides a necessary platform for subsequent analyses of embryology and metamorphosis.
基于连续的1微米切片、整体装片的光学显微镜观察以及扫描电子显微镜观察，对苔藓虫纲唇口目弯角苔藓虫（Watersipora arcuata）的幼虫进行了描述。使用轻度锇酸处理的标本，可以绘制出幼虫表面几乎每个细胞的图谱。结合解剖学描述，提供了关于孵化和幼虫行为的有限观察结果。幼虫的组织分为两类，一类仅在幼虫期发挥作用，在变态时作为过渡组织被降解；另一类在原肠胚形成过程中具有变态后的命运。值得注意的是，弯角苔藓虫有两个可能发育成原肠胚多毛体的原基，即口半球的冠下细胞和反口半球的表皮芽细胞，而不像其他物种那样只有其中一个。文中还详细描述了冠上凸缘和凹槽，它们是该属独有的，参与支原体样生物在成体连续世代之间的传播；两对复杂的色素杯眼点；多个冠间细胞，推测具有多种感觉和机械功能；以及梨形器官的感觉、附着和运动成分。将弯角苔藓虫的幼虫解剖结构与苔藓虫纲栉口目透明艾氏苔藓虫（Alcyonidium gelatinosum，有冠）、覆瓦鲍氏苔藓虫（Bowerbankia imbricata，有冠）、纤细鲍氏苔藓虫（B. gracilis，有冠）和粗糙格苔藓虫（Flustrellidra hispida，有壳卵黄营养型）以及唇口目苔藓虫纲的滨口苔藓虫（Bugula neritina，有冠）、毛状艾氏苔藓虫（Electra pilosa，苔藓虫幼体）和膜孔苔藓虫（Membranipora membranacea，苔藓虫幼体）的幼虫解剖结构进行了比较。本研究是对任何苔藓虫纲苔藓虫幼虫结构的首次详细分析，为后续胚胎学和变态分析提供了必要的平台。
