smaller MD-80 3x3 aircraft

I see some MD-80's in service now which looks to be between a CRJ and a normal size twin engine plane. Instead of the usual MD-88 3x2 format going up to row 36, these are 3x3, and have a much smaller capacity going up to row 22.

Where'd they get these planes from all of the sudden? Anyone know any info as to how long they've been in the fleet, and how many there are in total? These things are even smaller than the old DC-9's.

No listing anywhere about these planes on delta.com, seatguru, or anywhere. I see it on flt number DL 930

Thanks