Ranging from 100 to 200 microns across , the width of several human hairs , these microscopic fossils are surprisingly complex and constitute almost a textbook example of a bilaterian , including the three major tissue layers ( the endoderm , mesoderm and ectoderm familiar from high school biology texts ) , the presence of a gut with a mouth and anus , and paired coeloms ( body cavities ) surrounding the gut 这些微化石的大小为100 ~ 200微米，相当于几根头发的宽度， ?们看起来出奇复杂，而且简直就像两侧对称动物的教科书般，展示了各种特徵：包括三个主要的组织层（内胚层、中胚层及外胚层，都是中学生物课本中熟悉的名词） ，前后连接口部与肛门的肠腔，肠腔外还围绕著成对的体腔。
