Swimming in the Cambrian | ScienceBlogs
If you ever get a chance, spend some time looking at fish muscles in a microscope. Larval zebrafish are perfect; they're transparent and you can trace all the fibers, so you can see everything. The body musculature of fish is most elegantly organized into repeating blocks of muscle along the length of the animal, each segment having a chevron ("V") or "W" shape.
Source: scienceblogs.com