Let's now consider cnidarians:

Jellyfish have traditionally been considered simple and primitive. When you gaze at one in an aquarium tank, it is not hard to see why.

Like its relatives the sea anemone and coral, the jellyfish looks like a no-frills animal. It has no head, no back or front, no left or right sides, no legs or fins. It has no heart. Its gut is a blind pouch rather than a tube, so its mouth must serve as its anus. Instead of a brain, it has a diffuse net of nerves.

A fish or a shrimp may move quickly in a determined swim; a jellyfish pulses lazily along.

But new research has made scientists realize that they have underestimated the jellyfish and its relatives – known collectively as cnidarians (pronounced nih-DEHR-ee-uns). Beneath their seemingly simple exterior lies a remarkably sophisticated collection of genes, including many that give rise to humans' complex anatomy.

[...]

Much to their surprise, the scientists found that some genes switched on in embryos were nearly identical to the genes that determined the head-to-tail axis of bilaterians, including humans. More surprisingly, the genes switched on in the same head-to-tail pattern as in bilaterians.

Further studies showed that cnidarians used other genes from the bilaterian tool kit. The same genes that patterned the front and back of the bilaterian embryo, for example, were produced on opposite sides of the anemone embryo.
The findings have these scientists wondering why cnidarians use such a complex set of body-building genes when their bodies end up looking so simple. They have concluded that cnidarians may be more complicated than they appear, particularly in their nervous systems.

[...]

In some ways, cnidarians are a better model for human biology than fruit flies. As strange as it may seem, gazing at a jellyfish in an aquarium is a lot like looking in the mirror.

Here

But where shall we go from here?

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