All existing members of a pension system established pursuant to either Chapter 4 (commencing with Section 31900) or Chapter 5 (commencing with Section 32200) of this part and all employees eligible as safety members who at the time of entering service elected to become safety members, or who subsequently became members, shall become safety members and thereafter each person employed in a position, the principal duties of which consist of active law enforcement or active fire suppression or juvenile hall group counseling and group supervision, as defined in Sections 31469.3, 31469.4, 31470.2 and 31470.4, shall become a safety member on the first day of the calendar month following his or her entrance into the service. The sheriff and undersheriff shall become safety members on the first day of the calendar month following their entrance into the service. The marshal and assistant marshal shall become safety members on the first day of the calendar month following their appointment.