from recollection it either comes with the GSD or its inbuilt in that unit of plotter and doesnt need the GSD. i.e. all rangers have a depth sounder; its a shoot through hull option. if well installed it will see fish and hold bottom down to 700 feet.
i have the 5212 on my boat as its 2012 and it has the GSD 22. all boats use the same transducer. airmar p79.
some owners have chosen to add additional or replacement transducers - either through hull which requires making a large hole, or stern mount for trawling. but the standard unit when tuned does a good job.