The source for my interpretation of Vasto Lorde comes from Bleach anime 115, manga 197. From the latter (because it's easier to just type out Hitsugaya's lines from the comic page):
Menos are separated by three categories.
The first kind is a "Gillian." These are the weakest type of Menos. Comparing them to a human hierarchy, they would be considered soldiers. There are many of them, and they all look and act the same... (To Ichigo): The Menos you fought with shortly before entering Solu Society was a Gillian. They are gigantic but they're also slow and stupid...
The second class: "Adjuchas." They are smaller and more uncommon than Gillian. A Gillian's battle prowess and intelligence pale in comparison to one of these. The only thing the Gillians outweigh them in is sheer population.
Lastly, we have the third class: Vasto Lorde. They are the most powerful of any Menos and their size resembles a human more than any Hollow. Their numbers are unbelievably small and they are known only to exist deep within Hueco Mundo, but... the strength of a single Vasto Lorde is above that of any Captain.
In addition to that, we don't even know how many Arrancar there are in total... as of right now, including Aizen, if there exist over ten Vasto Lordes, Soul Society is doomed.
During the paragraph in which Hitsugaya talks about Vasto Lorde, the panel strongly resembles Ulquiorra in silhouette, and in the pages or anime scene immediately following Aizen welcomes Yammi and Ulquiorra back to their "twenty brothers and sisters." The implication is that the human shaped Arrancar that we've seen are all Vasto Lordes.
If I'm correct (and I may be on shakier ground here) being an Arrancar functions independently to whether or not you belong to the Adjuchas or Vasto Lorde class of Menos. When the Grand Fisher returned he seemed to me to be an Adjuchas that had been Arrancarised, as did Iceringer and Demora who weren't powerful or intelligent enough to gain human form (hence Ishida's taunting). You can be an Arrancar and not be a Vasto Lorde. Correct me if I'm wrong anyone.
Going back to that sequence at the end of the Soul Society arc, what appeared behind the Gillian seemed to be far larger, as though you were only seeing its eye opening or mouth smiling. It would seem to be something that we haven't encountered yet due primarily to its size, but it hasn't been referred to once since. Part of me wonders whether it has any connection to Hell, which we've been taught to view as a place entirely separate from Hueco Mundo. Soul Society and Hueco Mundo seem to be paralleled quite a lot in the subtext, so I've been speculating a little as to whether Hell and whatever realm the King inhabits also mirror each other. |