Sandworm

Nothing else on Arrakis compares. The sandworm is the planet's dominant lifeform, honoured and feared at once. Where the species came from nobody knows, only that it was there before the Butlerian Jihad. A worm lives beneath the sand and comes up after rhythmic vibration on the surface, because a steady beat reads as an intrusion on territory it will not share, and territory is the whole of its temper: two worms that sense each other trade chuffing roars of challenge and blow melange-smelling exhaust from their throats. Observers in the deep desert have reported specimens up to 450 metres long, against 33 metres for the largest animal of old Earth, and unconfirmed accounts put worms twice that near the southern pole. The skin is thick, rough and semi-metallic, built of interlocking scales a few feet across that armour the animal against the sand it moves through.