He says animals like sponges are even more ancient, but they lack the bilateral symmetry that characterizes most animals today.

示，海绵等动物更古老，但它们缺少现今大多数动物的两侧对称特性。

The scans confirmed the animals' bilateral body morphology and revealed the shape of the burrows they left from scavenging the seafloor.

扫描确认了动物的两侧对称身体态，并揭示了它们在海底觅食时留下的洞穴状。

Bilaterean body plans can be roughly divided into three sections.

两侧对称生物的身体结构大致可以分为三个部分。

Generally in the animal kingdom, once you evolve a bilaterally symmetrical body plan you don’t go back.

一般在动物界，一旦进化出两侧对称的身体结构，就不会再退回到不对称的状态。

And you have to remember the signals, the yellow ones that are bilaterally symmetric might be just the ones that are offering the best rewards.

因此， 你必须记信号，那黄色且两侧对称的， 可能正是提供最佳奖励的信号。

But starfish, despite being evolved from the same ancestors as other bilatereans, don’t seem to have an obvious tail, or head for that matter or clear symmetry.

但海星尽管与其它两侧对称动物有着相同的祖先，却没有明显的尾巴， 或者说头部， 也没有清晰的对称性。

And it’s an important piece of the puzzle when it comes to understanding bilaterean evolution and figuring out how strange creatures like echinoderms relate to creatures like us.

对于理解两侧对称生物的进化以及弄清楚像棘皮动物样的奇特生物与我们样的生物有何关联非常重要。

To settle the debate researchers mapped gene expression in different bits of starfish anatomy, looking specifically for the genes expressed in the forebrain, midbrain and trunk of other bilaterians.

为了平息争论， 研究人员绘制了海星不同部位的基因达图谱，特别寻找在其两侧对称生物的前脑、中脑和躯干中达的基因。