The TVTropes Trope Finder is where you can come to ask questions like "Do we have this one?" and "What's the trope about...?" Trying to rediscover a long lost show or other medium but need a little help? Head to Media Finder and try your luck there. Want to propose a new trope? You should be over at You Know, That Thing Where.
It would fall under Evil Is Visceral or one of its subtropes.
Time is subjective.
Organ Autonomy and Animate Body Parts come to mind. I don't believe, however, that "internal organ of a giant monster fought as a boss" is a trope we have, specifically. I'd call it a subtrope of both, personally.
If you do want to take this to the TLP, you've got enough examples already to meet the three-examples-minimum requirement, although they're need more context than they have here.
The Gomeramos King at the end of Contra, if you need more examples.
I'd like to apologize for all this.
a boss that is just a gigantic internal organ, usually of the big bad or whatever whale swallowed the protag, some examples I can list off the top of my head are:
is this a trope? and if not should it be?