Mental shield

A mental shield (not to be confused with the mutation Mental Mirror) is a property that makes creatures immune to mental damage and most mental effects, and blocks Telepathy. It is possessed by creatures without psionically accessible minds, whether because they are mindless (like most plants, fungi, and oozes), have artificial minds (i.e. robots), or are otherwise immune to psychic abilities.

The following effects cannot be applied to creatures with a mental shield:^[1]

As esper hunters

If the player has a high enough glimmer and summons a psychic assassin, there is a chance for the hunter to be a creature that normally has a mental shield. The shield is removed, and thus is normally affected by mental attacks and effects.^[2] Creatures with mental shields are unable to become psychic thralls.

List of creatures with a mental shield

Trivia

By default, robots, oozes, fungi, plants, and nests have mental shields. However, the mental shield is removed from sapient plants and fungi.

The only creatures with mental shields outside of those categories are girshworms, twinning lampreys, and trining lampreys.
Pax Klanq is the only fungus without a mental shield.
Euclid, and most of the members of the Consortium of Phyta (Yurl, Sixshrew, Tillifergaewicz, Asphodel, Earl of Omonporch, and asphodelytes) are sapient and thus do not have mental shields.
The oddly-hued glowpad, despite being a Consortium member and capable of speaking to the player, has a mental shield. It is the only Consortium member which does.