Because, osteostracans are among the few jawless fish to have a bony internal skeleton, or endoskeleton.

因为，osteostracans 是少数具有骨质内部骨骼或内骨骼的无颌鱼之一。

And it turns out, for every species with an internal skeleton like ours, Earth is home to around 20 species without one — and maybe more.

事实证明，对于每一个像我们这样有内部骨骼的物种来说，地球上大约有 20 个没有内部骨骼的物种——也许更多。

Once the cell has decided on a path, the other protruding probes are retracted using a kind of internal cellular skeleton made of microtubules.

一旦细胞确定了路径，其他突出的探针就会使用一种由微管制成的内部细胞骨架缩回。

On the other hand, or leg, our internal skeletons provide bigger attachments for muscles than exoskeletons would, and our bones grow with our muscles as we get bigger and stronger.

另一方面，我们的内部骨骼为肌肉提供了比外骨骼更大的附着，当我们变得更大更强壮时，我们的骨骼随着肌肉一起生长。

And it turns out, for every species with an internal skeleton like ours, Earth is home to around 20 species without one – and maybe more.

事实证明， 对于每一个像我们这样有内部骨骼的物种，地球上都有大约 20 种没有一个的物种——甚至可能更多。

And this arrangement is really interesting, because it combines both the normal, internal skeleton of the ankylosaur with the protective dermal skeleton to make a single structure.

这种排列非常有趣，因为它将甲龙正常的内部骨骼与保护性真皮骨骼结合在一起，形成一个单一的结构。

However, they didn't go as far as the Modern style, which is known as 'x-ray' because it actually makes a feature of the internal skeleton as well as the organs of animals and humans.

然而，它们不及“现代”风格。后者被称为“X光”，因为事实上它的特点是描绘了动物和人的骨架及器官。

But placoderms were also unique among armored fish in having a complete, mineralized internal skeleton – meaning they had both an endoskeleton, like you do, as well as an exoskeleton.

但盾皮鱼在有甲鱼中也是独一无二的，因为它们拥有完整的、矿化的内部骨骼——这意味着它们既有内骨骼，就像你一样， 也有外骨骼。

But there's no evidence that it had stereom - the stuff that makes up the internal skeleton of all echinoderms, so it could've just been another round animal like a jellyfish or a sponge.

但没有证据表明它有立体结构——构成所有棘皮动物内部骨骼的物质，所以它可能只是另一种圆形动物， 如水母或海绵。