There are 4 classes of anomalies, with each class having 10 levels from 1 to 10.

1 (Faction) Burrow / Drone Collection (lowest)
2 (Faction) Hideaway / Drone Cluster
3 (Faction) Refuge / Drone Gathering
4 (Faction) Den / Drone Gathering
5 (Faction) Yard / Drone Surveillance
6 (Faction) Rally Point / Drone Menagerie
7 (Faction) Port / Drone Herd
8 (Faction) Hub / Drone Squad
9 (Faction) Haven / Drone Patrol
10 (Faction) Sanctum / Drone Horde (hardest)

The highest level class is 'Forsaken'.
1, Sansha Burrow
2, Hidden Sansha Burrow
3, Forlorn Sansha Burrow
4, Forsaken Sansha Burrow