[jshepherd]

I can actually help you out with the meanings of these words in Japanese. I am not sure about the actual origin of Mabe and Akoya, and I do not think many Japanese would be sure either. This is because there is no 'kanji' equivalent of these words in Japanese that I know of. In other words, both 'Akoya' and 'Mabe' are spelled out phonetically in Japanese in either Hiragana or Katakana - I have never seen it written in Kanji (or characters of Chinese origin), giving the words a discernible meaning.
The other names, kurocho-gai and shirocho-gai are actually quite simple.
This is Japanese for Kurocho-gai:
黒真珠
These three characters mean:
Black (kuro) - Butterfly (cho) - Shellfish (gai)
So the black-lip oyster is the 'black butterfly shellfish' in Japanese.
Shiro, comes from 'shiroi' which, of course, means white!
So the white-lipped oyster (silver) is the 'white butterfly shellfish' in Japanese.
The 'Gai' is going to be after every name, such as Akoya-gai, etc., simply to denote the actual shellfish.