The first depiction of a sandworm with 3 radially-symmetrical mouth flaps I can find is an illustration by John Schoenherr for the first part of the serialized "The Prophet of Dune" in Analog, January 1965.
The same idea was used as the cover art for the third part in March of the same year:
Schoenherr refined this concept and the version of a sandworm shown on the 1978 Dune calendar was very similar to later depictions, including a ring of many inward-pointing teeth:
The worm's behavior toward Paul
What is that _thing_ in the beginning of Dune(1984)?
I’m sure this question has been asked many times before but: which sand worm do you guys like more?
Dune (1984) vs Dune (2021) Spice Harvester scene
Videos
The first depiction of a sandworm with 3 radially-symmetrical mouth flaps I can find is an illustration by John Schoenherr for the first part of the serialized "The Prophet of Dune" in Analog, January 1965.
The same idea was used as the cover art for the third part in March of the same year:
Schoenherr refined this concept and the version of a sandworm shown on the 1978 Dune calendar was very similar to later depictions, including a ring of many inward-pointing teeth: