A microcentrum cell membrane was a small region of cytoplasm near the nucleus of a cell that functioned as the dynamic center of the cell. Triolic waves would not harm species with microcentrum cell membranes, and those species were sometimes shapeshifters.
When evidence of triolic waves was discovered beneath San Francisco in 2368, Geordi La Forge suggested that the aliens may have been from Devidia II when he looked at the evidence available. (TNG: "Time's Arrow")