Nightmare Deep:Water Collossus

My Water entry to the Create a Colossus contest. I tried various different monster sketches until I came up with this, and am very happy with the result!

No time to color it, unfortunately, but I'll upload a colored headshot of it in a little bit, to portray the colors I - with the help of a wonderful friend - envisioned it as. I'm submitting the sketch as-is for now, with a background color that's easier on the eyes than pure white plus a little size-reference and comic relief. Fear the stick-figure of DOOOMMM!!!

Haha, anyway! A little about this guy here. The "spines" down his back, sticking out of his elbows and the "whiskers" (only one shown here) aren't usually stiff, but rather more like octopus tentacles, all hydrostatic muscle and very versatile and, yes, prehensile. They can, however, be filled with blood which, along with a special long-term muscular locking mechanism, allows them to become rigid with very sharp tips for both attack and defense. The membrane that creates the frill is highly elastic and slightly transparent, allowing shadowed silhouettes of objects behind it to be seen when there's light.

Now, the "wings." Originally, I had the membrane connecting all the way to the body, but after talking with Dad I changed it to reach just the elbows. This is because they use them to push and steer themselves, and if they had a big membrane then every time they opened their arms, it would billow out and create drag and really slow them down. Therefor, I modified it to what you see now: This form allows it to act as a modified flipper-wing, sort of like penguins but far more versatile, and even allows it more mobility due to the freedom of movement the lack of membrane gives the rest of the arm. The wings go from smallest near the head to the largest further down the body, with the fore-wings used more in steering and the hind-wings, along with vertical and occasional horizontal undulations of the body, are the primary providers of thrust in movement, though they all can serve either function just as well.
The "thumb" on each wing is full opposable, but would still be unwieldy due to the long, heavy talon at the end. Nevertheless, in tandem with their "spines" it allows them to grab and manipulate objects, as well as giving them another weapon.

This creature has extremely fine control over its body, and could easily pick up a fist-sized object using either talons or tentacles; even its tail-tips (yes, the tail splits in two) are somewhat prehensile, though a bit more difficult to use due to size. Its teeth are long, sharp and numerous, pointing backwards in its large jaw, which can unhinge much like a shark's or gulper eel's; each side of the lower jaw is connected only by muscle and ligaments, and can spread apart for maximum distention. The maxilla (upper "jaw") ends in a sharp, heavy-hooked three-pronged beak, and each side of the mandible (lower jaw) also ends in a talon-like upward protrusion.

The body has a large percentage of hydrostatic muscular structure, with an inner skeleton of cartilage similar in structure to a snake, with calcified keels attached via half-bone, half-cartilage ribs for the wing muscles to attach. The frill goes from the brow to just past the last wing, and picks up again just before the tail splits, as shown; the spine-frill starts and ends rather large, while the tail is much more gradual and ends just before the tips.

My favored coloration is a very, very dark forest-green for the body, a slightly lighter shade for the membranes, and a near-black green for the spines, beaks and last phalange of each wing-finger. The teeth and talons are white; the eyes have slit, reflective black pupils, with irises that take up the whole rest of the eye and transition abruptly between the teal of the background and a dark, dark blue-green. The extra "white" you see in either corner of the eye are actually its eyelids, which close horizontally rather than vertically.
I'm toying with the idea of it possibly being able to change its color, like an octopus, except even more advanced. If it doesn't win - which means I get to keep it! - I'm thinking I might add some crab-legs behind the last wing, and in the final color version have it sort of stepping off or climbing down an underwater cliff (*COUGHmountainCOUGH*). The illustration in the lower right-center shows a wing-flipper when it's both straight and bent. And if any of the frills look odd... Well, you try getting weird bend-y perspectives like that! 'Tis hard to make it look right!

I'll link the colored headshot and/or full-body once it's up.