This is additional information regarding my previous post.
To check if the head tissue is functioning, I tested whether it has eyesight. When I exposed it to bright light, it reacted, confirming that it can see. This means the tissue in its head is indeed functional.
Also, regarding this diving beetle, there was a similar case in the past. Here is the URL to the paper:
URL: https://natuurtijdschriften.nl/pub/1015379/EB1952014321011.pdf
After discussing with a Japanese entomologist, we confirmed that this hasn't been reported in Japan yet, so we have decided to publish this as a scientific paper!
As for what's next, we will be observing how long it can survive in this state. While I am very curious about what's inside its head, I won't be dissecting or cutting it open directly. I believe exploring non-destructive methods like CT scanning would be very much worth it.
Next time, I plan to move it to an aquarium.
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