Bet you didn't expect to see that! ;)
These are the wonderful, swirling, medusa-like tentacles of a terebellid worm, also known as a spaghetti worm. It's another species that we found recently in a Bull Kelp holdfast.
Here's a picture of the entire animal with its tentacles extended outward:
Whenever I see a terebellid worm like this, I think of the phrase, "Feed your head." I know that sounds strange, but it comes from a few summers ago when one of Eric's students created a music video with a terebellid worm and Jefferson Airplane's song White Rabbit (Nice job, Zander!). It was an excellent match, as the video footage of the worm's frenzied tentacles began to crescendo and peaked with the song's lyrics, "Remember what the dormouse said...Feed your head...Feed your head!"
And indeed, one of functions of the tentacles is to pull in food particles.
The tentacles are also used for gathering materials for tube building. And sometimes they help with locomotion.
In the next image, look for the tentacles that are expanded or flattened (they're broader than the others). The worm appeared to be using them as anchors. It would pull itself along in the direction of these "anchor tentacles" to shift into a new position. Doing this over and over (anchoring, pulling, anchoring, pulling) allowed the worm to cover substantial distances fairly quickly.
Although you can probably tell that I just love this worm's tentacles, here's a view of its body, too. It was generally bright red, with a bit of pink and yellow mixed in. We'll be consulting with experts about the specific identification.
P.S. If you were wondering, the red color in the tentacles is due to hemoglobin which aids in gas exchange.