David Beckham -- Spice Girls Reunite for 40th Birthday ... And Someone's Missing

The Spice Girls reunited for a very special occasion -- David Beckham's 40th birthday ... and someone was noticeably absent.

Victoria Beckham threw the party in Morocco Saturday and most everyone dutifully showed up, including Emma Bunton, Melanie Chisholm and Geri Halliwell. The missing Spice -- Mel B.

Victoria posted the pic and tagged it "Spice Girls in Marrakech!" ... thing is, Eva Longoria joined for the photo.

They didn't perform, but they partied with David's family and all the other celebs.