Probably the only set of models that I prefer an older style over the newer 4th. edition models.
The newer ones make the bodies a bit larger and the heads as well, but I like the head CARAPACE being so huge in comparison to the body. It really makes them look like floating heads, moreso than the new models ... and I love it. Also, the carapace shape looks more "Eldar-y" than the newer ones, and since the fluff indicates that Zoanthropes originated by assimilating Eldar DNA, I prefer this kind of look.
I painted them the usual purple exoskeleton with black carapace like the rest of my 'nids. Though as I painted these guys a while back (before 4th edition came out) I had this crazy idea of putting green spots on the purple exoskeletons to make them look more natural. It looked weird is what it did, and I've since tossed out that paint-scheme with the new models... though I don't have the heart to paint them off these guys. They're veterans, oldies ... I'll allow them their liverspots and blemishes. Adds character.
These guys are my Tyranid mobile Artillery. Since the new 4th edition rules allow me to give them more than one power (Thank The Emperor) I've equipped them with Warp Blast and Synapse Creature. Warp Blast is their main weapon, which I'll be using against heavy armor and vehicles. Synapse is because I may require a backup synapse creature. Due to my army leaning towards a "Zillanid" force, I imagine my opponent will target all my large critters as primary targets. That's fine with me, as I've allowed myself enough large bugs to make that a difficult feat ... also, I have enough numbers with the troops/Fast Attack, that focusing on my large guys will only spell my opponent's doom. The Synapse ability for the Zoanthropes is merely a precaution against a particularly crafty/lucky/well equipped opponent.