If your education includes substantial aspects of evolutionary developmental biology and genetics, then you have important mental models with which you can work with an organism. If you discover that the whole organism is effectively developmentally a head, then it is extremely appropriate to refer to it essentially as a head.
If you instead relate to the organism in its present form in some more mundane ways then it might not seem that way.
Analogies are failing me, but perhaps it would be like realizing an entire government basically spawned out of the centering concept of religious freedom. The structure of it then makes a lot more sense.
I'd say that whale flippers are homologous to legs/feet, but aren't legs/feet. This article says that starfish are homologous to heads, but I'm not sure whether I'd consider their bodies to be heads or not.
This discovery is to our understanding of starfish what Georges Cuvier’s discoveries of vertebrate morphology were to your present understanding of whales.
If you instead relate to the organism in its present form in some more mundane ways then it might not seem that way.
Analogies are failing me, but perhaps it would be like realizing an entire government basically spawned out of the centering concept of religious freedom. The structure of it then makes a lot more sense.