Not Found on Most Oak Trees - Saccoglossus sp.

We're not sure how Hemichordate worms get the name "acorn worms" but this photo of a species belonging to the genus, Saccoglossus, seemed to be enough to drive our audience nuts. Also called proboscis worms, or tongue worms, hemichordates like this species live burrowed in soft muddy sediments or in shell sand where they feed by probing out from their burrown with their soft flexible proboscis. The mucus-generating organ traps detritus particles which are transported up the proboscis to the mouth on the front edge of the collar (the brighter red section in this photo). Behind the collar, the worm's body has a series of gill slits.

Hemichordates are relatives of the Echinoderms and the Chordates; all are placed together on a major branch of animal life, the deuterostomes. Many evolutionary biologists think that modern Hemichordate worms resemble some of the ancient ancestors to chordates - a split that took place at least 500 million years ago.

Check our gallery on animal phyla.