Among young main sequence stars surrounded by debris disks, a handful of remarkable objects exhibit a substantial amount of primordial gas, making them hybrid disks between proto-planetary and debris disks: 49 Ceti (40 Myr, Zuckerman et al. 1995; Moór et al. 2011), HD 21997 (30 Myr, Kóspál et al. 2013), HD 141569 (5 Myr, Dent et al. 2005), and HD 131835 (16 Myr, Moór et al. 2015).
