Again no screenshots. I took them this time, they just weren't particularly great.
I had the green catacrab:
Easy enough to find - travel to Orgrimmar, take the portal to Blasted Lands and fly off to the coast.
The first thing I noticed were the animations - they're the same as the shale spiders. Or rather, the shale spiders are the same as the crabs: I checked later with a vanilla crab (my starter crab, Stupidface) and they're identical. I leveled 1-10 with the starter crab and never noticed it. Shows how much I usually pay attention to these things
The swimming animation is quite nice and realistic, in my opinion - the crab will use both its legs and its pincers to push forward in the water. Looks very smooth and natural.
As for the model... it tames quite large, at least by goblin standards. It was almost as tall as I am, although that might be an impression helped by the large spikes on its head. It's a nice, forest-y green - blends in quite well in grassy areas, such as Nagrand. And it's quite ugly, actually, in a cute, endearing sort of way. I'd never tamed one of these before (with the exception of Ghostcrawler, but he's all transparent and stuff). They look old to me - probably because of the spikes around the mouth. Kind of like old, wise, annoyed sages, all

at being constantly sent into battle by clueless young whippernsappers. (Whereas the vanilla crabs, to me, look like they're always saying, "butbutbut... butbutbut... why me?" - although that might be an impression I get just from looking at Stupidface and pondering abandoning him, but feeling too guilty to.)
I specced the critter for pure tanking and went to kill a few things around my level to test the aggro-holding. It's as good as your average tenacity pet,
if you take the family special off of autocast. If you don't, it'll channel Pin first thing rather than building threat, and if you haven't killed your enemy by the time the channel's over it'll come over and eat your face. (The enemy, not the crab.)
This is annoying. I don't mind tenacity pets with non-survival family specials (I love my green catacroc as much as I love my beetles and turtles), but I'd like to at least be able to
use the damn special rather than take it off autocast and forget it exists. Mind you, I don't PVP, so I don't know if the skill might be more useful there.
In the end, I let this one go. I already have one crab I don't want to abandon but never use due to the special being godawful, I don't need a second one. If it had a more useful special, I might've kept it, though - I liked how it looked with my character.