Unfortunately I don't have enough time to do more dios I have a few oldies, I will post them if you like.
As for the water effects, I love to experiment. Believe me, I have tried many things. In this case, I took two grainy B/W pictures of the Liop and the Ophthalmo. I'm holding the Liop so it appears to be swimming. After that, I resized, cut and pasted the Ophthalmo. Then I added a fake shadow and I coloured the pic.
The effects aren't secret. I just play around with Photoshop. I guess I could write a tutorial for some but others are old and I can't even remember what I used exactly Besides, I had a full version of Photoshop 6 back then, now I have a 'light' version.
New dio, several Cretaceous cephalopods:
Explanation: I actually took seven different pics, (six of the animals, one of the background) and put them together. For the background I used a slab of volcanic rock. You have to cut them very carefully, otherwise it will look terrible. It should look a lot better with a decent camera (the Polyptychoceras have an awful whiteness I couldn't remove). A friend of mine told me it wasn't convincing, but I couldn't do better. I used an almost transparent dark blue layer (the opacity of the colour is %5 if I recall correctly, you can modulate it with Photoshop and get different results)