Spherical and aspherical are generally terms used to describe a lens property, not the resulting image. I only know of one circular fisheye for the Pentax (or any cropped sensor for that matter), the Sigma 4.5mm.
Flickr: Sigma 4.5mm f/2.8 EX DC Circular Fisheye
This lens has a full circular field of view of 180 degrees. The exposed image is a circle.
The Pentax 10-17mm isn't circular. The maximum field of view of this lens is 180 degrees only at the diagonals. The image is rectangular.
Full-size sample photos from Pentax 10-17mm F/3.5-4.5
It's always a fisheye and, as such, always produces lots of distortion. However, as reeftool mentioned, at 17mm this distortion is reduced (compared to 10mm). I personally wouldn't characterize the distortion at 17mm small, but I would also say, depending upon the image, most people would have a difficult time differentiating between a wide angle and the fisheye (@17mm).