@Pheno: Yes, you're right, the middle one has some banding, and very noticeable at 2x or more! :/
Thanks everyone else for your comments!
These are superb! My favorite has to be the horseshoe crab.
I love crustaceans, and these ones are excellently pixeled! Looks to be a little bit of very noticeable banding on that middle one (or maybe just ineffective pixeling), but otherwise very good work.
Man, thanks for discovering me the Anomalocaris, what a design!! Now I want this instead of a Cintiq --> http://ecx.images-amazon.com/images/I/41XPHYvd0tL._SX300_.jpg
Wow, Alberto, these are outstanding! Pretty much perfect little sprites.
What I would give to see some critters from ancient times pixelled by you. Like an Anomalocaris, Megalograptus, Pterygotus or even a Jaekelopterus.
These are super effective and delicious!