Seahorse model with segmented tail.
Paper & size
Start with the white side up when folding with a two-colored paper. The head of the seahorse will be white, but this can be prevented by making the outside reverse fold in step 10 not with two edges at each side, but first moving an edge to one of the sides (so you end up with three edges on one side and one edge on the other).
When folded from a 17.5cm square, the resulting model ends up about 13.5cm in height and 8.5cm wide.