All proper nouns need to be capitalized. I believe you are puzzled over whether "Asian" is a proper noun or not. I don't see why not. We need to define what a proper noun is:
A proper noun or proper name is a noun representing a unique entity (such as London, Jupiter, John Hunter, or Toyota), as distinguished from a common noun, which represents a class of entities (or nonunique instance[s] of that class)—for example, city, planet, person or corporation).
Now, I believe you think that "Asian" is too broad a noun to be called a proper noun, because it seems to represent a class of entities, that is, a group of various people, such as Spanish, French, etc.
Does that mean, however, that we shouldn't capitalize "Europe", but should just write it as "europe"? Of course not. "Europe" still refers to a specific place, a continent, and "Europeans" refer to a specific people, the people that come from Europe. And there's only one group of people that comes from Europe, the Europeans.
No. None of these are trademarked terms. A tablet PC is a type of computer. It's not a brand or model name. It should only be capitalized under special circumstances, like if it's in the title, included in a model name, or at the beginning of a sentence.
Best Answer
It depends on which level of taxonomy that term is. For genus and higher, names are capitalized. Species and terms more specific than species (like variety and subspecies) are not capitalized.
Thus, for your example, Crustacea should be capitalized because it is a subphylum.
More details can be found here.