In the Crystal Isles, there's a large floating island with a massive river. There's at least six of them throughout that river. Get a couple high level aquatic or amphibious tames, I use a max level baryonix and Deinosuchus (modded), but a sarco might work. Don't just bring one creature, these things have no issues teaming up on their prey. Anyway, EXCELLENT resource for chitin and organic polymer, best I've found yet! Beware, though, you're not safe just because you're hovering over the water on a flyer, those things can JUMP!
I’d say I’m having pretty bad day. So, I just bought Abberation and I was so excited, so I went over to the water. I don’t know much about Abberation, so I thought the Karkinos was just a kind little crab. Oh boy was I wrong.. I went closer to the water, as I was thirsty. But the Karkinos comes running up to me, picks me up and shreds me to pieces. Let’s just say I took a little break from Abberation 1 minute after I bought it.
killed an alpha with my x-allo and only lost 1-2k health, compared to the allo’s over 20k health total. These things are pretty easy to kill if you have a good creature, and are an amazing source of polymer and chitin.