Will post more if I find more.
New Trailer (Full version of the limit break teaser):
There are lots of hi-res screenshots taken from the trailer released from SE:
Arcanist:
Arcanist is a pet class using Carbuncle.
Arcanist weapon is a Book.
Multiple "types" of Carbuncle: a "tank" carbuncle and a "caster" Carbuncle.
Arcanist focuses on debuffs and DoT.
Arcanist is to be in the game at launch
Summoner:
Summoner summons "essences" of Primals to fight for them.
More "types" than Arcanist/Carbuncle. More powerful pet actions.
Summoner won't make it for launch and will be added in a patch shortly afterwards.
Notes:
SE were not specific on mechanics for this class/job. My guess is that Arcanist will be a class where you partner with Carbuncle, who is out all the time, kind of like BST. While Summoner will be more focussed on calling essenses to perform attacks (and then released due to huge MP drain) like it was in FFXI.