Vertebrate body

The most obvious aspect of an animal body is that of mouth-stomach-anus or head-body-tail mediated duality.
Mouth-stomach-anus aspect would be the first to evolve for any living entity.
Life starts with birth and then eating and growth follow.
If you can't eat, you can't grow, very simple.
Eating can be as simple as in and out of a simple tube, like worms suggest.
A particular eating action evolves as a low entropy solution to many types of action that a differentiated population would use.
An eating action would have to controlled from the front since sensors would be there.
The first sense for an animal to experience would be taste.

The second most obvious aspect is left-middle-right mediated duality.
L/R seperation is necessary since most movements would have to be in a plane for a water-land margin living entity.
With head/tail and left/right setup, we are ready to navigate a plane.
A certain type of head/tail, left/right oscillation would be enough to move.
This motion would be the one that splits the first animal brain.
Then we get many appendages appear, as worm evolution shows, and these settle to head/tail, left/right and arms/legs configuration for vertebrates.

These steps map to M0-2;
SM0=1/1=1 ... mouth/anus (head/tail)
SM1=1/2 ... left/right
SM2=2/4 ... arms/legs

To continue.