Wiktionary
placode
n. A platelike thickening of the epithelial layer of an embryo from which an organ, especially a sense organ, develops.
Wikipedia
Usage examples of "placode".
Deducing that these differing portions represented the same placode text, the cryptanalysts compared the two messages until, in a single afternoon, they found a transposition and blank arrangement that yielded the same texts in a form that resembled legitimate codewords.
This machine would then compare the placode groups with the decode cards in its storage and print out the plaintext for whatever decode cards it had.
Code that has not yet undergone such a process—called superencipherment —or which has been deciphered from it is called placode, a shortening of "plain code.