Evolutionary developmental Biological study of Acoela, Turbellaria

1. 为了使正常的表发育在一个小涡虫，卷叶虫。用扫描电镜观察胚胎发育过程。胚胎在受精后约90小时孵化，整个过程分为16个阶段。表皮细胞和下面的肌肉细胞呈复杂的结构，没有中间的基底结构。为了解肌表皮复合体的形成是否变性所致，采用透射电镜对复合体形成的发育过程进行了研究。肌-表皮复合体形成于胚胎发育早期，在肌-表皮复合体的形成过程中未出现基底结构。3 .对9目涡虫的18s核糖体DNA进行分子系统发育分析，发现涡虫属中最原始的一种。对7目湍流虫线粒体密码子进行比较，除Acoel外，其余6目中AAA和ATA分别编码天冬氨酸和异亮氨酸，而Acoel中AAA和XPA分别编码赖氨酸和蛋氨酸。这一事实表明，在其他湍流体被指定之前，气团就已经分化了。

1. In order to make the normal table of development in an acoel turbellarian, Convoluta naikaiensis. the process of the embryonic development was examined by scanning electron microscopy. The embryo hatched about 90 hr after fertilization and the process was divided into 16 stages.2. In the acoel, the epidermal cells and the underlying muscle cells show a complex structure without an intervening basal structure. In order to knpw whether the muscle-epidermis complex results from degeneration, developmental process of the formation of the complex was examined by transmission electron microscopy. The complex was formed in the early stage of the embryonic development and the basal structure never appeared during the course of the muscle-epidermis complex.Molecular phylogenetic analysis on the basis of the 18s ribosomal DNA using 9 orders of the turbellarians revealed that the Acoela is the most primitive in the turbellarian.4. Mitochondrial codons were compared among 7 orders of the turbellarians, In the 6 orders except the Acoel, AAA and ATA code aspartic acid and isoleucine, respectively, but in the Acoel, AAA and XPA codes lysine and methionine, respectively. This fact suggests the Acoela diverged before other turbellarians were specified.