BOOBOO: people think this means "ASIA," but it doesn't. A while ago, just as a pun, some Japanese decided to spell the word "ASIA" phonetically, using kanji, like so: 亜細亜：あじあ: but this custom never caught on. And besides, the 亜 kanji was only chosen for its sound, not for its meaning.
亜 is used in a lot of names of elements, like chalk or zinc, but unless you're a research chemist or terrorist, this doesn't concern you.
亜熱帯：あねったい： subtropical region
See what I mean?
As for the shape, I got nothing!
Well. . . there's a net and what looks like a roman numeral II. So if you're an ancient Roman, you have your regular net which you use to catch your prey, and if that breaks, then you have your #II net, a sub-net, which you keep in reserve.