Gozo Shioda says in one of his textbooks that the hand should be open with the fingers apart "like a Morning Glory flower". This is (perhaps not surprisingly) what Kanetsuka Sensei teaches too. All the Aikikai shihan I have seen keep the fingers open.
I don't think I have seen anyone demonstrating with the fingers together. Are there any examples on YouTube of this?
"Always open your hand like a morning glory ("asagao")"
And here's one by Yukiyoshi Sagawa that I think has not generally been made available in English:
I was told by Takeda Sensei to open my hand in the way that a Morning Glory ("Asagao") blooms, but I think that this means to open the hand while rotating slightly. I conceived of my Aiki while thinking about this kind of thing.