Evolutionary developmental Biological study of Acoela, Turbellaria

1.为了建立内海涡虫的正常发育表。用扫描电子显微镜观察胚胎发育过程。胚胎在受精后90小时左右孵化，发育过程分为16个阶段。在Aacel中，表皮细胞和下层肌肉细胞显示出复杂的结构，没有中间的基底部结构。为了确定肌肉-表皮复合体是否是退变的结果，用透射电子显微镜观察了该复合体形成的发育过程。该复合体形成于胚胎发育的早期，在肌肉-表皮复合体的形成过程中基本没有出现。基于9目涡虫18S核糖体DNA的分子系统发育分析表明，Acoela是涡虫中最原始的。比较了除Acoel、AAA和ATA编码的天冬氨酸和异亮氨酸外的6个目的线粒体密码子，而Acoel、AAA和XPA编码的赖氨酸和甲硫氨酸的编码分别为赖氨酸和甲硫氨酸。这一事实表明，Acoela在其他涡轮虫被指明之前就出现了分歧。

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.