Egg Sack or what?

[KelnKelp]

Hey All... saw bunches of these guys two weekends ago at Channels dive site of Anacapa Island, Southern California. They were anchored in the sand getting blown back and forth by the surge. About a foot long, looked really thin and possibly transparent-ish though they were covered with sand. Curious as to what they are. Thanks! -K

 

[PhilC]

Looks like the discarded mucus coating of a burrowing anemone to me but I don't know if they have similar creatures on the left coast.