Favoritos de thetidepooler

Happy to find this population still here. Four individuals, each with unique patterning. Two of each under separate rocks (1 & 2, and 3 & 4). They have grown quite a bit since being observed by @ltimmo. The yellow spots on the mantle seem to be a feature present on all individuals.
Looking through previous observations it seems these can take on the colours of their prey ascidian to an extent. With these being purplish and see:
https://inaturalist.nz/observations/214917318 (the botrylloides here were golden yellow)

1,2,3 ~ 2 cm long 4 ~ 1cm long.
Shallow subtidal

Edit: G. castanea?

Apata cf. pricei of Behrens et al. (2022), Coleman Beach, Sonoma Co., CA, 29 Apr 2009. 15mm length.

CASIZ 181322 (as Flabellina)

Photos by Gary R. McDonald (@mcduck) of a specimen I found in the low rocky intertidal in the morning, collected, kept cool and then dropped off in Aromas, CA for Gary to photograph using his home aquarium setup, which he did that evening. Gary later relaxed and preserved the specimen and sent it to the Invertebrate Zoology collection at the California Academy of Sciences. Scanned from 35 mm slides.

Brenna Green (@lemurdillo, who had joined me for the low tide) and I were looking at this specimen in the field after I found it and were perplexed by its identity. We decided it was closest to Flabellina pricei (now Apata pricei), but the differences in color from the few other specimens of F. pricei I had seen, warranted its collection, and I labelled the specimen as Flabellina (pricei?).

iNatting with @emma_brockes.
Both length 4 mm when extended.
Low intertidal. Found by sieving through red algae and brown algae (Image #5 #6) growing on a wall of a shallow crevice on the reef.
Placida?

Undescribed species, 22 mm long. I spotted this specimen on its flat, coiled egg mass (also see 2nd image) on a pebble grabbed with gray mud from 186 m depth off Cape Alava, WA while on a cruise AR-04-04 of the NOAA Ship McArthur II in June 2004. The translucent dorsum was finely scabrous to the touch. The 4th image is an SEM, made by Sandra Millen (UBC), of some of its radular teeth. Sandra confirmed this as an undescribed species and last I heard had been well along in describing it. The first three images were scanned from prints I took shipboard using 35 mm film. The specimen, including two SEM mounts, was deposited by Sandra Millen in the California Academy of Sciences (CASIZ 176807).

Only a few mm long; found on Codium fragile. Unlike Placida dendritica, this undescribed species has simple (not rolled) rhinophores. It appears to be the same species as specimens I found earlier in the same year on Codium fragile at Punta Rosarito, Baja California (http://www.seaslugforum.net/showall/stilsp1). Scanned from prints from 35 mm film.

Eubranchus sp. 2 of Behrens & Hermosillo (2005). Found by Ziggy and the first record of this species outside of La Jolla. Compare to: https://www.inaturalist.org/observations/2958115

In Behrens et al. (2022) this is Eubranchus sp. 1.

6.8 mm long. Found in a shallow, low intertidal pool at South Casa Reef. CASIZ 189422.

This is Eubranchus sp. 2 of Behrens & Hermosillo (2005), which so far is only known from La Jolla, California and remains undescribed. Note: in April 2021 we found one at Tar Pits Reef in Carpinteria, Santa Barbara County: https://www.inaturalist.org/observations/75602522

The white patch on the head, reddish hepatic region, white anal papilla, and rings of papillae on the cerata are distinctive.

The 3rd and 4th images show egg masses, containing early and late-stage embryos, respectively, laid by adult pictured here. The last image shows a newly hatched veliger larva, right lateral view, with a shell 210 microns long.

La Paz, B.C.S., Mexico
Three of these, found together under a rock with sparse hydroids. Each only about 2-3 mm - quite small. At first, I thought they might be odd Tenellia albocrusta. (B.C.S. is the southern range limit of C. albocrusta according to Gary’s iNat guide: https://www.inaturalist.org/guide_taxa/933633#ref2)

But the thing that gave me pause was how extensive the opaque white speckles are - extensively down the oral tentacles (not seen in any other photo of C. albocrusta on iNat) and the entire length of the rhinophores. All three had the same markings.

In Camacho-Garcia, Gosliner and Valdes, “Guia del Campo de las Babosas Marinas del Pacifico Este Tropical,” 2005, p. 105, a tiny Cuthona Sp 6 looks like a possibility - the photo isn’t reproduced well, but there seems to be white on the oral tentacles (not mentioned in the text, so I may be seeing something incorrectly) and white spots on the rhinophores are mentioned. I haven’t seen more recent information on this Cuthona.

From TGosliner: "This looks like something entirely new to me! It certainly is not Tenellia albocrusta. The head shape and ceratal color are entirely different. Very cool!"

missing a tentacle and a little roughed up

undescribed species, first intertidal observation im aware of!
https://www.inaturalist.org/journal/nudibitch/88226-mystery-flatworms-black-midline-black-tentacles