This species occurs on Bodega Head, but recently I was able to obtain a few nice photos in Pacific Grove:
A coral with tentacles expanded. Individuals are 7-15 mm in diameter.
A coral completely withdrawn into its skeleton. (The 12 white squiggly lines appear to be the skeletal partitions, called septa.)
The skeleton of a cup coral viewed from above. This specimen was found on Bodega Head.
These calcareous skeletons may be found washed up on beaches. Note the large openings (or chambers) where the cup corals brood their embryos. When fully developed, relatively large (3-5 mm long) demersal (bottom dwelling) larvae are released. These planula larvae crawl along the bottom for just a few days and usually attach to a rock within 40 cm of the parent. Most larvae are released during late winter.
Cup coral habitat in Pacific Grove (adjacent to a site known as The Great Tidepool to Ed Ricketts/John Steinbeck).