Invertebrate · GBIF taxon 2292241
Horned Nudibranch
Hermissenda crassicornisAlso known as Opalescent Nudibranch, Thick-horned Nudibranch, Opalescent Sea Slug
Horned nudibranchs are striking Pacific sea slugs recognized by their iridescent blue body lines and translucent, orange-tipped cerata. These aggressive carnivores actively hunt hydroids and anemones, storing their prey's stinging nematocysts inside their own bodies for self-defense. When two individuals meet on the seafloor, they frequently clash in fast-paced combat, biting off each other's cerata.
MarineColorfulCarnivorous
—observations
—countries
—peak records
Not EvaluatedConservation statusIUCN Red List categoriesLCNTVUENCREWEXNot Evaluated — not placed on the risk ladderRed List categories, explained →
Diet & prey
- Hydroids
- Sea anemones
- Bryozoans
Predators
- Sea stars
- Kelp crabs
- Navanax
ThreatsCoastal runoff, ocean warming, habitat loss
HabitatsRocky intertidal zones, tide pools, shallow reefs, marina pilings
Life span1–2 years
Size / weightNot available
Classification
- FamilyMyrrhinidae
- SpeciesHermissenda crassicornis
Range data is not available yet.
Interaction riskLow
- Low
- Moderate
- High
- Very high
- Why interaction risk is low
- Safe to observe in tide pools; avoid touching to protect delicate tissues.
Responsible observation
- Tide Pool Etiquette: Observe underwater without lifting the animal out of damp substrate.
- Spotting Strategy: Scan submerged hydroid colonies where they frequently hunt and feed.
- Lighting Tip: Use a diffused dive torch to illuminate their opalescent blue stripes.
Similar Sea Slug NPS Photo / Public domain · cc0
Competitor (c) Ken-ichi Ueda, some rights reserved (CC BY), uploaded by Ken-ichi Ueda · cc-by
Close Relative (c) Steve Addison, some rights reserved (CC BY) · cc-by
Help improve the field guideSomething wrong?
Checking your Fauna account…Report a name, category, or profile issue for review.