Also known as Burrowing Worm, Sand Worm, Worm Cast.
Found buried under the sand with their castings on top. They live in shallow waters in a U shaped mucus lined burrow in the sand, sometimes hidden under stones and shells, rarely seen out of the sand.
Length - 100cm
Depth - Under the sand
An acorn worm's body is made up of three sections: the proboscis, collar and trunk. The proboscis is connected by a short stalk to the collar which contains the mouth, this is also used for burrowing in the sand.
The rest of the worm is made up of a long trunk that has gill slits. Oxygenated water is drawn in through the mouth and expelled through the gills. In this way, the acorn worm breathes with part of its gut! 'Enteropneusta' means 'gut breathing'.
The acorn worm's skin is densely covered with cilia (tiny hairs) and glands which secrete a mucus that covers the body. Some produce a bromide compound that gives them a medicinal smell and might protect them from bacteria and predators.
These worms swallow mud and sand and process these for edible bits of plankton. At low tide, they stick out their rear ends at the surface and excrete coils of processed sediments. Called the cast, this is all that most people will see of an acorn worm! (edit) Ref: https://en.wikipedia.org/wiki/Acorn_worm