Eric and I have continued our survey of Bull Kelp holdfasts. This nudibranch is one of the most recent discoveries. Three-lined Nudibranchs (Flabellina trilineata) are fairly common along local rocky shores, but this is the first time we've encountered one in a holdfast.
Here's a close-up of the cephalic (head) tentacles, with white stripes and orange tips...and the rhinophores (chemosensory organs), with their wonderful spiral structure. [When rhinophores have this shape they're formally called lamellate or perfoliate.]
I was struck by the bright orange tips to both the tentacles and the rhinophores. Sometimes this species has orange tips, and sometimes it doesn't.
The "three lines" in both the common name and the scientific name come from the white lines running down the back and along each side of the nudibranch. It's hard to see all three in one picture. This view shows the dorsal (top) stripe and one of the side stripes:
While the next image shows all three: the dorsal stripe between the cerata (orange/red projections) and the two lateral stripes converging at the posterior end of the foot.
Most of the Three-lined Nudibranchs I've seen in this area have been between 1-2 cm in length and have been associated with hydroids. When they're around, their combination of white and bright red-orange coloration is hard to miss!