Thanks for the comments, John.
In the initial planning and sketching stages of this, the effect that I was after was for the creature to be as disconnected as possible to the structural design of the animal species we're familiar with. I didn't want someone to look at it and easily associate it with any kind of animal on the planet. It's supposed to be an alien, after all.
The head and face design was kind of tough and went through a couple of revisions because I wanted, like I said above, it to be as alien as possible. I also tried to make it as simple as possible as well, in order to deal with the difficulty of recognition that results from those design goals. (Plus, I have to admit that I was flying by the seat of my pants most of the time; I'm by no means experienced with 3DCG)
The creature is ultimately going to be drawn by hand in a comic by someone else, so my next step is going to be to provide a breakdown into the base geometric construction forms. Before I do that, I'd like to have the design nailed down as much as possible, so if you could elaborate on the changes you think would help, I'd appreciate it.
About the tentacles: the idea with them was that they would be retracted most of the time and then would shoot out suddenly to grab the target, holding on just long enough to be shredded by the scythe-like arms. So, I intentionally left them looking soft and smooth in contrast to the rest of the creature's body, as I envisioned them to be rubbery and flexible, not too tough. I suppose they could stand a treatment of some detail, but if so, it won't be the same type as the main body. I'll work on that. I'll also come up with a new pose or two to illustrate the mechanics of how they would shoot out to grab.
To answer your questions on how it moves, my idea was to make the underside look like tire treads so that it could slither along like a cross between a snake and a snail. Also it has definite segments to the tail part so that it could fold like an accordion and lunge forward in a sudden burst. Hope that makes sense.