The part missing is an oil sump grommet. They are removable for flywheel inspection. If you are mostly highway not a big deal to have one missing. But you don't want to wade of fling mud up in there. You can get one from the stealership for 30 bucks or Atlantic british has a genuine LR part for 12. I replaced mine when I did the front cover job. Here is a link to the part at AB

Oil Pan Grommet (Rear) - Land Rover gaskets and seals from Atlantic British