Aerobatic parachutes are slightly different as they have the buckles moved so that they are not underneath the aircraft straps. You can use a standard parachute, but you will get bruises from the straps digging the buckles into you.
Most sport rigs today don't use buckles, or use a minimum thereof. Pilot emergency canopies are typically round canopies, though some ram-air square parachutes are now in use as emergency rigs.
Sport rigs take a little more training and one shouldn't wear one during aerobatic flight as a pilot without proper training in the wearing, and use. Unlike an emergency rig, there are more handles and controls and more ways that the parachute (either one) may be released in the airplane...which can be a deadly event. There are also more ways to disable or make unsafe a sport rig than a pilot rig. Pilot rigs are lighter, flatter, and easier to wear when getting in and out of the aircraft.
Today's sport rigs tend to utilze very small canopies which make the overall container smaller, but also lead to more injuries and fatalities while flying and landing a perfectly good parachute. Nobody should wear a parachute aloft without adequate training in normal and emergency parachute operations, malfunction recognition and clearing, egress, water and tree landings, parachute landing falls, and perhaps most important to the pilot, protecting the rig from deployment in the airplane.