Ants digging.. hmmm
It could be done with a cell type which isnt algea but is rock (no feeding valeu) of solid color (maybbe a lot of .shell only)
Rock would be a bit hard to digg i mean kill (like requiring a special shot type), a shot type that would also have more effect on .shell
Rock would normally be fixed pos (however as some animals use rocks as to their protection.
In essence a solid rock needs a default fixed state (but once shot at a few times becomes free to move). (might be attracted by gravity)
A smart animal would use this as shielding... (or even collect it for shielding).
Oh and rocks dont duplicate, might split by shooting into smaller rocks.
But so far i've never seen a rock in an act of replicating.
Also they dont have vision
So .. they are almost like a raw basic cell no memory regions no DNA execution(* perhaps for splitting a little command),
maybe some different rocktypes (hard harder, soft, seize, maybe squares or circles or hexagons, or simple triangles.).
Except for the non round shapes Could be done in current DB
But DB engine could be optimized for them in a next version, since they require far less computation.