realy cool designs, I can't help with the anatomy, cause I couldn't have done this any better. But here is how I would try to make them look even cooler, try to get in a bit more shadow to indicate more volume. I did a couple of rough sketches to get the idea across a little better :)

Complete beginner here, so please don't put too much weight on my opinion. I think you were going for disturbing H P Lovecraft-ish creatures here, and I think you succeeded there. They are very creepy looking. Good job. I don't know enough anatomy to have an informed opinion, but I have some impressions. In the first picture, the attachment area of the tentacle heads and the body could be smoother. Also the weight of figure falls on the slug body and you don't see it squished down flatter. I also feel it could come forward a bit to balance the weight of the ball out better. The second picture is nice. I think it is flying, so I feel like the wings could be spread out more as if in flight. But you may have been thinking of a different action, such as landing. The third picture is cool. I like the twist in the body which really shows off the worm like nature. I like the position of the back rear leg, but the front leg's position in the background is a little unclear. Given the shape of the one in the foreground, would you be able to see more of the one in the background? What if it was raised in a striking position. Please take whatever helps you from my reply and throw the rest away.