Artist Leslie Newell with her son Devan, 22, at Old Port Sea Grill in Portland, where her work is on display. (Derek Davis/Staff Photographer)PORTLAND — Laura Argitis has never displayed artwork for sale in the 23 years she has owned the Old Port Sea Grill. “My name is Devan Newell and my Mother Leslie has Parkinson’s disease and uses artwork as a form of therapy. She’s been using a walker, but when she arrived at the Old Port Sea Grill on Wednesday, she ditched it when she saw Argitis. One piece at the center of the display at Old Port Sea Grill is a heart shaped out of mussel shells.