Sorry for the slow reply. I wanted to do some checking before I replied. Great questions by the way!

1. This discovery provides evidence for the argument that X(8372) & Y(4360) should be interpreted as 4-quark systems, where each contain at least one charm and one anti-charm quark. To my understanding, it is a description that best fits the data and is *also* verifiable. I answered number 2 first and inadvertently wrote a few things relevant to this question there.

1.5. To be honest, this is the first time I have ever heard of that term. According to Wiki’s definition, I suppose a “mesonic molecule” might qualify as an exotic hadron. However, I am not a particular fan of the phrase because, to me, the term “molecule” implies an electrodynamical bonding and not chromodynamical. Like in chemistry, molecules exist because of the bonding is due to an exchange of electrons; so chemical bonds are electrodynamical in nature. Hadronic structures exist due to the strong force and not electrodynamics. Lastly, to me the difference between “tetraquark” and “4-quark” systems is whichever sounds better in a particular sentence.

2. Wikipedia is a great source of information; but at times it does not contain up-to-date information about a scientific discovery, if a part of it is still open to debate. Rightfully so, I might add. There is zero evidence for 5-quark systems. For 4-quark system, there is growing evidence. In fact, I decided to write this post after realizing that KEK laboratories had previously discovered 10 other exotic hadrons (http://www.kek.jp/intra-e/press/2012/011014/#term07 – The link will take you to a specific part of the press release to which I refer in the post.). The scientific consensus that is forming is that these 12 exotic hadrons are actually 4-quark systems, which is unexpected but not forbidden by current models.

2.1 Regarding previous QD articles, the only other post that comes to mind is a great piece by Aiden (http://www.quantumdiaries.org/2011/10/10/who-ordered-that-an-x-traordinary-particle/), where he addresses this specific debate. One strong argument regarding 4-quark systems is if they exist, then they there should be other exotic hadrons that contain non-charmed quarks, e.g., bottom quarks. Belle’s discovery is precisely confirmation of this argument.

Spot on. In chromodynamics, the charge is collectively referred as “color”; this is 99% analogous to the electric charge in electrodynamics. The difference is that in chromodynamics, there are three different possible charges for a single quark, whereas for a single electron, there is only one possible charge.

For example in electrodynamics, an electron always possess an electric charge of -1, and an anti-electron (aka a positron) will always be a charge of anti-”-1″, which is sometimes called +1.
And in chromodynamics, a top quark, for example, can be found with a “red” charge, a “blue” charge, or a “green” charge; an anti-top quark can posses an “anti-red” charge, an “anti-blue” charge, or an “anti-green” charge. Additionally, the top quark still has a +2/3 electric charge, and the anti-top quark has a -2/3 electric charge.

If I recall correctly, the color mapping goes as:
anti-red = cyan
anti-green = magenta
anti-blue = yellow

However, this is simply a convention and is inconsequential to the physics. Personally, I just say “anti-red/blue/green”.

1) Does this shed any light on the mysterious X(3872) or Y(4360) particle? I recall those and their other weird friends were thought by some to be candidate exotic hadrons.

1.5) Is a so-called “mesonic molecule” the same thing as an exotic hadron? If deuterium is an example of a hexaquark, as you say, then I would think so.

2) Wikipedia says tetraquarks and pentaquarks are still both hypothetical. In fact, previous articles on quantum diaries site have implied as much. You say that these are about the 12th tetraquarks that have been discovered. Am I misunderstanding something here?