The lurker den and lurker, as well as the base hydralisk strain, are exclusive to Kerrigan in Co-op Missions. The lurker den and lurker are unlocked when Kerrigan reaches Level 5. Ecxept the multiplayer, the lurker den morph into hydralisk den. Upgrades for the lurker become available when Kerrigan reaches 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.