Great question!
This specific drain is by ProLine QuickDrain and the stainless grate is considered to be the strainer. From ProLine, "Quick Drain systems are very easy to clean. The drain cover is removable and even the waste pipe is accessible for cleaning whenever needed."
For more information, here is the ProLine strainer website: http://www.quickdrainusa.com/linear-drain-covers-strainers.php
We also install a drain called quARTz by ACO (photo below) and they have an optional hair strainer that fits into the drain body below the stainless grate.
A word of caution: if a hair strainer is used below the stainless grate, be certain to keep it free of too much debris. If not kept clean, the water could potentially back up into the shower because an unclean hair strainer can block water from going down the drain.