原肠动物

例句：

1. 1. The discovery of the first multicellular organisms was a major breakthrough in thestudy of evolution.
   首次发现多细胞生物是研究进化的一个重大突破。
2. 2.In the early days of life sciences, scientists were puzzled by the fact that some animals could reproduce without the need for sexual union.
   在生命科学的早期，科学家们对一些动物不需要性结合就能繁殖的事实感到困惑。
3. 3. The concept of "protostomes" has since been expanded to include all forms of life, from unicellular tomulticellular organisms.
   “原肠胚”的概念后来被扩展到所有形式的生命，从单细胞到多细胞生物。