What is "plakobranchus"

Plakobranchus is a genus of sea slugs, sacoglossans, marine opisthobranch gastropod mollusks in the family Plakobranchidae.

The author of the genus spelled the name originally as Plakobranchus, but the spelling Placobranchus was a long time the prevailing usage, based on an incorrect subsequent spelling by Férussac (1824) in a translation of van Hasselt's work.