Anti-ground defense structure
The sunken colony is a zerg structure that protects their hive clusters against ground-based attacks. Rooting itself deep into creep via rows of sharp teeth, the colony grows multiple tendrils that it can use to attack any enemies that come within range. The impaler colony, a creation of the Overmind, was the ancestor of the sunken colony.
Sunken colonies deal explosive damage. This makes them more potent in the later game when higher tier medium- and large-sized units appear. The colony has a slower rate of fire than the photon cannon which further reduces its effectiveness against small units, which tend to appear in larger numbers. On the other hand, the colony is much more durable than the photon cannon.
Sunken colonies have 300 HP as opposed to the 400 HP of the creep colony. When one morphs, if the creep colony's remaining health was 101 or above, then 100 points are subtracted from it. If the remaining health before morphing was 100 or below, it is kept instead.
This article or section contains information about StarCraft: Ghost, which has been declared non-canon. Elements may be taken as 'flavor lore' however.
The following section contains information from a previous version of StarCraft II which is no longer valid.
The sunken colony moved on crab-like legs outside of the boundaries of creep, but like other zerg structures would slowly degenerate and eventually die if it remained outside of the boundaries for too long. It could not plant itself outside the creep, however.