Edit- The Gruul Keyrune has a horn on it, with an anthropomorphic face... Maybe there're Rhox on Ravnica now? It's worth a guess. Also, the Simic Keyrune, of course, looks very deep-sea-ish. I'm thinking a kraken, though probably a very small one.
Additional edit- Firstly, an initial glance at the Dimir Keyrune makes it look as though it's Batman's own keyrune. But upon further investigation, it appears to have an arachnid figure crawling down it.
...My God. You're right. The plating resembles the head ornaments of cards like Cephalid Retainer. The tentacles also fit.
Cephalids returning would be the single greatest thing RTR could bring for me.:D
Cephalids were explicitly very Dominarian. Also, Simic just got merfolk, another blue tribe that we didn't see last time. The chances of the Cephalid thing happening I believe are very, very low.
However, let's think of what Cephalids are based off of. Squids and octopi if I'm right. What would be a great thing for a UG keyrune to change into? A squid or octopus would be pretty good. Or a very small kraken.
The point is, Cephalids aren't coming back, at least not in this block.
Zegana looks a little tentacly, maybe tentacles are a thing of Simic waterlife? Kraj was also a little on the tentacle-side, so the Simic aren't new to the thought of suckers.
Perhaps the tentacled ones were some how more protected from Kraj when all hell broke loose so that's who's running things down there now. Also: Boros keyrune is obviously an Iron Man Sword. For those moments when he just wants to slice and dice instead of blast everything to pieces. (I'm hoping we get a boros card that can be altered into Iron Man without just completely changing the art)
There you can find these "new" pics :). There are also a lot of other matherial like wallpapers. I think it worth to download the one from your guild.
Also, just in case you did not notice; in the "Advance Search" page in Gatherer (http://gatherer.wizards.com/Pages/Advanced.aspx) now you can search the cards of your guild selecting the "mark" entry (The one that before only contained Phyrexia/Mirran)