Scaled Tube Snail (Thylacodes squamigerus, formerly Serpulorbis squamigerus)
Although I first introduced tube snails (vermetid gastropods) several years ago, the individual shown above is a different species that I haven't yet shown on the blog.
Scaled Tube Snails are a more southern species — they're rare in Northern California. I photographed the snail in the picture above in the rocky intertidal zone on 21 February 2016. It was relatively small, so we're wondering if it's a younger animal, perhaps recently arrived with the warm water during the last couple of years.
Here's a different individual that I photographed on 9 April 2012:
Note the pretty orange band at the opening of the tube and the lack of an operculum (trap door). The other species of tube snail in this area, Petaloconchus, is much smaller in size, lacks the scaly texture on its tube (see first photo above), and has an operculum.
For an introduction to this fascinating groups of snails, review the post from 11 June 2012, and the video on 17 March 2015.