paramecium (n.)

"genus of holotrichous ciliate Infusorial" [OED]; "the slipper-animacule" [Century Dictionary]; 1752, Modern Latin Paramecium, the genus name, coined from Greek paramekes "oblong, oval," from para- "on one side" (see para- (1)) + mēkos "length," related to makros "long," from PIE root *mak- "long, thin."