The basic life of the seasquirt is to be born and then find a place to take root. This is the hardest job it does in its life, find a place to hang. Once the seasquirt has found a place then it takes a hold of the rock and sets about reducing its brain size. It really does this, it has done the hardest thing it will ever need to do so it casts off this unwelcome baggage of excess brain that after all will just consume power for nothing.
On reducing brain size the seaquirt takes to squirting. It is basically a tube shaped muscle that sucks in sea water and squirts it out again. In squirting, all of the nutrients it will ever need are pulled into its body and all of the unwanted waste is expelled. Its whole body is mouth, gut and, well, the mouth is also the anus.