Idanthyrsus cretus Chamberlin, 1919. A) Entire worm, dorsal view, B) same, ventral view, C) abdominal uncinus dentition, lateral view, D) abdominal uncini, E) operculum and parathorax, F) nuchal hook, G) outer opercular paleae, H) inner opercular paleae. Scale bars: A) 2 mm, B, E) 4 mm, C) 1000x magnification, D, G–H) 400x magnification, F) 0.25 mm.