Exequias

The are Arrancar that form an execution division in Sōsuke Aizen's army of Arrancar.

Outline
They are responsible for dealing with rebels and intruders in Las Noches, usually terminating both hence their name.

The Espada, much like with the Números, seem to have a level of control over the Exequias, though the extent of their control is uncertain; Szayel Aporro Granz had ordered them to kill the intruders that had entered Las Noches and to retrieve the of the defeated Privaron Espada. After being summoned by Szayel, the Exequias proceeded to act under Rudobōn's command.

Rudobōn reveals to Rukia that the special ability of his Zanpakutō, Arbol, allows him to create the underlings who are seen following him. This explains why they all have identical masks and Zanpakutō. Technically, Rudobōn is the sole member of the Exequias, with the other members merely being his creations with no individuality seen thus far.

Uniform
The uniform of the Exequias is the custom white jacket and hakama worn by all Arrancar in Aizen's army. All Exequias however have the same skull-like mask. Rudobōn's seniority is reflected in the different mask he wears compared to the human like skulls of his subordinates.

List of Exequias

 * Rudobōn: Sole member of the Exequias.
 * Calaveras: Calaveras comprise the entirety of the Exequias, being produced by Rudobōn.

Dispensability
It seems as though the Exequias are all created from Rudobōn's special ability, that creates as many soldiers as he likes. This means that the Exequias are created at will by his Zanpakutō, which explains their identical uniforms and masks. The soldiers aside from Rudobōn are therefore completely dispensable, which he mentions to Rukia: "You will soon find that defeating my underlings is not the same as defeating me" (he then releases Árbol.)