* Hollow: This is most common type among the population in Huceo Mundo. They have a White mask which is used to block out emotions and procet the raw instincts. They have a hollow in their chest showing their heart/love is gone. Their body takes a new form(ex like a snake or pig or somthing else but not a human body form) The more powerful ones tend to have a special power. Like Gran Fisher with his puppet or something like being able to shot acid.

* Menos are created By Powerful hollows eating other powerful hollows of the same type.Those hollows nartual congregate togther.For more deatils on it and the other class go to the link below.There the mutal feasting begains and they meld together into one.These composite entities can be enormous, and pose such a serious threat to both the living and the dead that the Soul Society has had to create highly trained strike teams devoted just to handling Menos incursions. In chapter 197 of the manga, three classes of Menos have been revealed: gillian, adjuchas and vasto lorde but reference on how the three classes of meons are made go to http://manga.bleachexile.com/bleach-chapter-284-page-7.html
and read all of chapter 284.

It is important to note the difference between the Menos and the arrancar status. All Menos are classified into one of the three classes; arrancar simply signifies if a hollow has removed its masks or not. Thus, it is possible to have a pure Menos, a non-Menos arrancar, or an arrancar who is based on a Menos.

* Gillian (girian) - the weakest class of Menos, they are large and physically strong but not agile, and don't have much brain power. They are formed when many hollows merge together, and though much more powerful than an average hollow, they are still much weaker than a shinigami captain. In Soul Society gillians are known as Menos Grande, and are shown in textbooks discussing Menos.

* Adjuchas (ajūkasu) - smaller but smarter than the gillians, they are thought to be far superior. It is likely they could fight evenly with at least a shinigami lieutenant. This type of Menos is much smaller in population compared to the gillian class. They also have the power to order many Gillian like a commander comanding his units.If the Adjuchas is killed or leaves the battle ground the Gillian stop working together and starte doing their own thing which could mean to contuine fighting(very unlikly) ,dispears, or just stand there and scream.

* Vasto Lorde (vastorōde) - the top fighters of the Menos with an extremely small population who are believed only to exist within the very depths of Hueco Mundo. They have a more humanoid appearance than the other classes of hollow. Each of them is stronger than an average captain; therefore, Tōshirō Hitsugaya claims that 10 is enough to defeat all of the Soul Society. Soul Society does not have definite information on the number of vasto lorde, and it seems that Sōsuke Aizen has important plans with them which hasn't been revealed as of yet.

* Arrancar they are hollows who have removed their mask in order to gain some Shinigami powers. The hollow that tend to do this are among the Meno's class of Adjuchas and above. The more human like the Arrancar the more poweful it is. When they release their blade they transform back most into what they look like as a Meno's along with their special powers they had as a Meno's