Shalka

The Shalka are an alien race encountered by the Alternative Ninth Doctor in the web-based episode Scream of the Shalka. They are made almost entirely out of lava and have no set form. The ones shown were large worm-like creatures with cobra-like frills, but there were also Shalka of different sizes and shapes.

They live underground, near where lava meets metamorphic rock. They communicated by screaming, and breathed volcanic air; the only exception was Prime, the Shalka leader, who was able to speak and breathe normal air. They use sound as a weapon and a means of controlling "lower alien creatures," among other uses.