The lurker den and lurker are exclusive to Kerrigan in Co-op Missions, and become available when Kerrigan reaches Level 5. The structure is available in the Lair phase of the game to allow the morphing of lurkers. However one difference with the Versus mode structure is that the co-op lurker den morphs in from a hydralisk den, instead of directly from a drone like in Versus mode currently. Finally, the structure can research an upgrade for the lurker to increase their range once a Hive has been produced, which also requires Kerrigan to be Level 6.
Prior to Patch 4.0, the lurker den was still mutated from a hydralisk den. The "Digging Claws" upgrade was announced.
Patch 4.11 decreased the lurker den build time from 86 seconds to 57 and readded the scrapped Seismic Spines upgrade, increasing the lurker's attack range from 8 to 10 rather than 6 to 9 and taking 57 seconds to research instead of 80. The build time for Adaptive Talons was increased from 54 seconds to 57.