A bit about the process: Each image went through maniputation in Adobe Photoshop. The images from the video probe miscroscope were originally in color, but I decided to make them greyscale to better fit with the black and white images from a Scanning Electron Microscope (SEM). The page and cover backgrounds are close-ups of a pigeon feather captured with an SEM. See below for details on each creature image.
The Existentialsaurus started as a video probe microscope image of a purple sea urchin. The "eye" is an air bubble caught in soft tissue, which is attached to a shed sea urchin spine. The spheres in the background are sea urchin embryos in the gastrula stage. The Existentialsaurus's features were created through photomanipulation in Adboe Illustrator, and was converted to greyscale in Adobe Photoshop.
Speinder started as two video probe microscope images of a purple sea urchin spine with different focuses. After combining the two images and creating the features of Speinder in Adobe Photoshop, it was converted to greyscale. 
Ploddrain started as an SEM image of pollen on a flower from a pink powderpuff tree. I upped the contrast, edited out the magnification guide, and drew the eyes and mouth in Adobe Photoshop.
Bickerbranch started as an SEM image of a plant from the genus anthurium. I used Adobe Photoshop to up the contrast and create faces. 
Cragrab started as an SEM image of a pigeon feather. I used Adobe Photoshop to add contrast to the image, and used a combination of collage and digital drawing to make Cragrab.
Just So Stories: Microorganisms is meant to be a small 16 page book, printed on one two-sided sheet of glossy cardstock (and then cut appart and bound with staples). Here's what the pages look like when arranged for printing: