A drawing of an acorn worm (Ptychodera flava) from New Caledonia.
Date circa 1911 .
Source A. Willey, "Balanoglossus" in Hugh Chisholm, ed., The Encyclopædia Britannica (11th ed.) (Cambridge: Cambridge University Press, 1910–1911).
Author Unknown author.
Source: https://commons.wikimedia.org/wiki/File:Ptychodera_flava_in_New_Caledonia,_from_Encyclopaedia_Britannica_(1911).png

Ptychodera flava, also kown as yellow acorn worm, belongs to family Ptychoderidae. It was first described by Johann Friedrich von Eschscholtz in 1825.

Order: Enteropneusta
Family: Ptychoderidae
Genus: Ptychodera
Species: Ptychodera flava Eschscholtz, 1825