I see Orion with the belt 'above' M42 from north skies but since down there you are saying 'below' I take it you mean north in declination as 'below'.
You describe 3 stars in a row running through it so that is almost certainly the running man as that has a row of stars right in the nebula and from up north the dark areas are described as a man running and taking a jump over the stars with spread out legs. You would have to 'flip' that image.
There is 'The Running Man' which has enough texture in it so that maybe you envisioned a sea horse in that nebula. The Running Man is a bright nebula with a complex but fairly big darker area runing throughout it for about 20 minutes length which is rather big as deepsky objects go but far smaller than the massive M42 size.
There are thousands of pictures but a quick look for one that highlights the darker area well I see this one where north is to the left so what you would see is this picture rotated 90 degrees CCW (approximately)
http://eldoradostarparty.org/ngc-197...of-waco-texas/
Again, your description really sounds like this which is also called Ngc1975 or the cluster part of it is called Ngc1977
We have been getting skunked with clouds for this week and maybe even through the new moon. Glad you have nice skies
Mark Johnston