Hermissenda crassicornis (Eschscholtz, 1831)

Description

A very colourful aeolid with a translucent grey-white body. An orange to yellow band runs along the dorsal midline, flanked on each side by an iridescent blue line and a white line. Numerous orange-brown cerata are clustered along the back, their tips tinged white or blue. It grows to about 5 cm. It is well known as a long-standing model organism in the neuroscience of learning and memory.

Distribution

Northeastern Pacific, along the west coast of North America from Alaska to California. It occurs in a wide range of habitats — rocky reefs, sandy bottoms and eelgrass beds — from the intertidal zone to the shallow subtidal. The species was originally described from Alaska.

Etymology

The specific epithet crassicornis is Latin for “thick-horned” (crassus, thick + cornu, horn), after the stout tentacles.

Remarks

A voracious predator that eats hydroids and also small anemones, other sea slugs, carrion, and even members of its own species. It was long treated as a single wide-ranging North Pacific species, so that Japanese animals were also called Hermissenda crassicornis; a 2016 study showed that western Pacific (including Japanese) populations belong to a separate species, Hermissenda emurai. The two look very similar and are reliably separated only by molecular data.

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References

• Cavolina crassicornis n.sp., Eschscholtz F. (1831). Zoologischer Atlas, enthaltend Abbildungen und Beschreibungen neuer Thierarten, während des Flottcapitains von Kotzebue zweiter Reise um die Welt. Heft 4: 1-19. G. Reimer, Berlin.
• Hermissenda crassicornis, Lindsay T. & Valdés Á. (2016). The Model Organism Hermissenda crassicornis (Gastropoda: Heterobranchia) Is a Species Complex. PLOS ONE. 11(4): e0154265. https://doi.org/10.1371/journal.pone.0154265
• Hermissenda crassicornis, Behrens D.W., Hermosillo A., Fletcher K. & Jensen G.C. (2022). Nudibranchs & Sea Slugs of the Eastern Pacific. Molamarine.