Lay a purple ribbon

At the end of field work in the rocky intertidal zone on Bodega Head yesterday morning (28 May 2013), I peeked under a ledge to see this scene:

 

There's a lot going on the picture above, but pay particular attention to three things: 

(1) the two pale blobs — these are nudibranchs (sea slugs)

(2) the O-shaped purple ring between them — this is an egg ribbon

(3) the bright pink surface in the right half of the photo — this is a sponge

Below are two close-ups of the nudibranchs.  Sorry that these aren't better photos, but you can still see that they are predominantly white with scattered yellow spots.  Interestingly, one of them has more yellow spots than the other.  This could mean that they're different species, but unfortunately I didn't have time to check more features to be certain.  They both appear to be species of Cadlina.

 

 

The next image is a close-up of the egg ribbon.  I'm wondering if one of these nudibranchs laid this egg ribbon.  I can't be sure, but it looks like it was produced recently, and there's often a "guilty-by-association" phenomenon with nudibranchs and egg masses.  I hadn't seen an egg ribbon this color before, so it seemed worth documenting.

 

It was interesting to see how well the egg ribbon blended in with the color of the sponge.  Nudibranchs in the genus Cadlina are known to eat sponges like this.  I don't know if the nudibranchs were feeding on the sponge, but it's a possibility.

 

P.S.  Click here for a better photo of Cadlina luteomarginata taken on Bodega Head last May.