As the organisms that players can create jump up in complexity from a single cell to many cells, it would seem out of place for the bodies of long organisms such as worms to remain rigid. For this reason, it could be worthwhile to implement 3d skeletal bones that deform the mesh, and allow the organism to wiggle from side to side and possibly even improve locomotion speed through passive forward undulations.
Not only would this improve the realism of the simulation and allow the creation of complex body structures that are useful for the creature’s survival, it’d also improve how the shape of your organism impacts it’s speed and movement efficiency through water, something that mirrors real life multicellular developments. This could also serve as practice for the implementation of limbs through a similar system, where groups of cells in limb-like formations gain their own bones that enable limb flexibility. Additionally, cells and tissues that the player adds in strategic locations might alter the movement style of the skeletal bones, allowing for more flexible movements in return for some cost, either of space or resources.
This might also be possible to add to creatures in the cell stage, but would probably make the most sense in the multicellular stage due to the presence of many specialized and overlapping cells allowing for more flexible, worm-like movement compared to that of single cells. This sort of feature would be a core aspect of more complex designs down the road and so is likely a keystone feature that should be implemented early on, and adding it at the start of the cell stage would kill two birds with one stone - preparing the game for future skeletal mesh mechanics, and allowing the late cell stage and early multicellular stage to represent animals that are as true to life as possible.
In my opinion, it would be a shame to be unable to make a creature that moves around like this:
