Tidepool Tim says,  “Hemichordates like the acorn worm are a small phylum with large evolutionary importance!  It's worth carefully recovering these worms from their burrows for research and educational purposes.  Another familiar group of hemichordates is the graptolites, well-known index fossils often used to date rocks (biostratigraphy).

Acorn worms have classic hemichordate triple body division and use their proboscis to burrow through the sediment.  They can either suspension feed (in water) or deposit feed (in sediment).  Acorn worms are difficult to collect because they're extremely thin and fragile bodies break if they are disturbed."