19.1.5 File System Mounting, SunOS 5.X
For remote file systems the default is specified in the file /etc/dfs/fstypes, and is set to nfs.
When using the mount command these defaults are assumed unless otherwise specified, e.g. by using the -F option:
# mount -F file-type file-system mount-point
The actual mount command used and the available options are determined by the file-type specification. The man pages for mount_ufs, mount_nfs, mount_hsfs, mount_rfs, and mount_tmpfs describe the options available. The actual commands are located in /usr/lib/fs under subdirectories named for the file-types.