Medell's teammate Johnny Birch Jr. earned bronze for a total of three American medals.
Team USA athletes closed swimming competition with 62 medals – 14 golds, 16 silvers and 32 bronzes – in Lima.
Shafik earned his first Parapan American medal in Toronto in 2015.
The U.S. men are seeking their fourth consecutive Parapan American Games title.
Mayhugh led Team USA to a 5-1 record and bronze medal in Lima.