Board Thread:General Discussion/@comment-4041418-20140315151044/@comment-4620155-20140316020042

it's most likely that:
 * Espadas 1-4 are Vasto Lordes
 * Espadas 5-8 are Adjuchas (recall that Aaroniero is the only Gillian amongst the Espada)
 * Yammy is an Adjuchas who just happens to have an overpowered ability. I don't think he's a Vasto Lorde because:
 * he is able to release his form inside Las Noches whilst 1-4 can't.
 * he's simply too fat.