These pictures were taken at very high magnification under a microscope. I'll zoom out a little more for a slightly broader view:
And here's another picture that's very similar, but from a slightly different angle (below).
Any guesses yet? The long feathery structures (tentacles) may be a helpful clue.
I can also tell you that both the tentacles and the unusual funnel-shaped pod that's filled with tiny objects with red spots can be withdrawn into a calcareous tube (visible as a white blur in the background).
The next image will give the answer away, so only look further if you're ready.
These are small spirorbid tubeworms. Their feathery tentacles are fanned outward when feeding (capturing plankton from the water). Spirorbid worms have a funnel-shaped operculum that seals the opening to their tubes when the worm pulls in. In some species, including this one, the operculum doubles as a brood chamber for their embryos!
The tiny objects in the operculum with red spots are developing embryos. The red spots are eyespots (two per embryo). The embryos will develop in the operculum for ~2-4 weeks (depending on the species and water temperature), and then will hatch as larvae and swim briefly before settling down to form their own tubes.
Here's another example of a tubeworm with extended feeding tentacles and an operculum filled with embryos.
If you've spent some time near the shore, you've probably seen spirorbids, but you may have walked by them without a second glance because of their small size (only a few millimeters across). But they're quite common on rocks and seaweeds (or hard-shelled animals such as mussels and snails) and sometimes occur in dense patches:
On 6 February 2012, I showed pictures of a different species of spirorbid from Bodega Head (see those images here). I'm still trying to work out the identification of spirorbids that live in this region, so we'll have to update you as we learn more. For now I hope you enjoyed learning a bit about their life history!