Ink and brush is a technique I picked up when I started drawing comic art in art school. Previously I swore by Sakura Micron pens, and while I still use those for scientific illustration, brush and pen (with exchangeable nibs) dipped in Speedball Superblack Ink are now my preferred drawing tools. I've tried mimicking the effect of brush and ink using computer drawing tools, but the feel nor the look are the same, so far. Not that this hermit crab hasn't been computer modified - it's been Live Traced in Illustrator, which nicely smooths gritty scans.
I'd been asked to spruce up a set of worksheets for aquarium classes. The current versions had a few bits of clip art thrown in as an after thought to liven up the page. Unfortunately, often the clip art was poorly suited for the purpose - for example, a photo of a sea urchin appeared to be a smudged dust bunny due to poor resolution. My illustrations, based on photos, are made with mass duplication in black in white in mind, as well as the potential for coloring with fat crayons. I try to strike a balance between accurate representation and whimsy, with personal art style and aesthetic composition thrown in. It's not about duplicating a photograph of a hermit crab - it's about extracting the essential elements from the photo (or several photos) that are most important in conveying the idea of a hermit crab, and interpreting those to form a new image.