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Northern Opalescent Nudibranch

Northern Opalescent Nudibranch

HAPPY MUG MONDAY!!! 🥳

This week we’re welcoming to the stage the absolutely 🌈radiant🌈 and ✨️breathtaking✨️ Northern Opalescent Nudibranch (Hermissenda crassicornis), also known as the Thick-horned Nudibranch. These divas belong to the sassy and shell-less family Myrrhinidae, which consists of the aeolid nudibranchs which are quite literally nudibranchs that do not have a shell. The stunning individuals in Myrrhinidae are tiny yet captivating divas from the sea, and the Northern Opalescent Nudibranch is no exception to this. You might need to whip out a magnifying glass to see all of the moves this diva is whipping out on stage – while the boots might be small, the house will be boots’d DOWN, honey. H. crassicornis is not to be mistaken for its sister species, H. opalescens, which lacks the stunning white stripes marked on their ceratas (literally Greek for “horns”). While they look extremely similar, they are not the same species but do still represent the same biological drag family (take notes, Michelle 💅). You can find the Northern Opalescent Nudibranch here on the Oregon coast in tide pools, as it ranges all the way from Northern California up to Alaska. Its sister, H. opalescens has a range of overlap in Northern California where you can see these species posing together for gorgeous family photos. When the tides are low, definitely go exploring for these divas and they will not disappoint.

Pictures, Resources and More Information:

  • Lindsay T & ValdésÁ. (2016). The Model Organism Hermissenda crassicornis (Gastropoda: Heterobranchia) Is a Species Complex. PloS One. 11(4):e0154265. doi: 10.1371/journal.pone.0154265
  • MolluscaBase eds. (2026). MolluscaBase. Myrrhinidae Bergh, 1905. Accessed through: World Register of Marine Species at on 2026-03-30

Published

March 30, 2026

Mug Monday