I found a crack in he undercarraige of my car that concerns me. Photos attached. It doesn't "feel" weak or unstable, but I realize the car puts just a tad more pressure on this than my hand can reproduce. What is the name of this particular component and should I be concerned? For context, in case the pictures aren't clear, this is just behind the differential housing between the rear wheels.

Attached Thumbnails

   

__________________
1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)