Mass Effect: Return from the Shadows
The volus are an associate race on the Citadel with their own embassy, but are also a client race of the turians. They hail from Irune, which possesses a high-pressure greenhouse atmosphere able to support an ammonia-based biochemistry. As a result, the volus must wear pressure suits and breathers when dealing with other species.
Because they are not physically adept compared to most species, volus mostly make their influence felt through trade and commerce, and they have a long history on the Citadel. However, they have never been invited to join the Council, which is a sore point for many volus individuals.