Ruiz-Trillo I, Riutort M, Littlewood D T, Herniou E A, Baguña J
Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain.
Science. 1999 Mar 19;283(5409):1919-23. doi: 10.1126/science.283.5409.1919.
Because of their simple organization the Acoela have been considered to be either primitive bilaterians or descendants of coelomates through secondary loss of derived features. Sequence data of 18S ribosomal DNA genes from non-fast evolving species of acoels and other metazoans reveal that this group does not belong to the Platyhelminthes but represents the extant members of the earliest divergent Bilateria, an interpretation that is supported by recent studies on the embryonic cleavage pattern and nervous system of acoels. This study has implications for understanding the evolution of major body plans, and for perceptions of the Cambrian evolutionary explosion.
由于组织简单，无腔动物被认为要么是原始两侧对称动物，要么是通过次生丧失衍生特征而从有腔动物进化而来的后代。来自无腔动物和其他后生动物非快速进化物种的18S核糖体DNA基因序列数据表明，该类群不属于扁形动物门，而是代表最早分化的两侧对称动物的现存成员，这一解释得到了最近关于无腔动物胚胎卵裂模式和神经系统研究的支持。这项研究对于理解主要身体结构的进化以及寒武纪进化大爆发具有重要意义。
