A 19-year-old Eureka man was arrested in Petaluma Saturday night after police found a loaded handgun in his car with the serial number removed. Royce Justin Moorehead was arrested for possession of a loaded firearm and possession of a firearm without a serial number, police said. His passenger, Juan Quintero, was cited for possession of marijuana and released. Police saw Moorehead and Quintero sitting a parked car behind the Henny Penny restaurant at 4995 Petaluma Blvd. North at about 11:55 p.m. Saturday. Officers searched the car and found a loaded handgun under the front seat. The gun’s serial number had been removed. Police said they also found gang paraphernalia, a box of ammunition and marijuana.Moorehead, who police allege is a gang member, was booked into Sonoma County jail. Bail was set at $10,000.Police said the case is still under investigation.