Muscular Augments
Source: Hydralisk Den
Minerals: 150
Vespene Gas: 150
Research Time: 100
The Hydralisk moves at a decent pace and attacks from range, so this upgrade isn't terribly important. However, if you plan to attack with a large swarm of them, then consider researching it.
Grooved Spines
Source: Hydralisk Den
Minerals: 150
Vespene Gas: 150
Research Time: 100
This upgrade will increase the Hydralisk's attack range to 5. A greater attack range is always good and since Hydralisks are used in most Zerg bases, this is definately worth getting.