"Young Balanoglossus: showing proboscis, collar, gill-slits, and gastric region. Balanoglossus, a worm-like animal of much zoological interest as a connecting link between invertebrates and vertebrates." -Hazeltine, 1894

Acorn Worm

"Young Balanoglossus: showing proboscis, collar, gill-slits, and gastric region. Balanoglossus, a worm-like…