Tritonia exsulans

Images courtesy of Kevin Lee
Point Dume, California

Image courtesy of Kevin Lee

Tritonia exsulans Bergh, 1894

A couple of our local Pacific coast Tritonia's have undergone name changes in recent years. Tritonia exsulans is now what we called Tritonia diomedea for years.

Martynov (2006, 2009) suppressed Tritonia diomedea Bergh, 1894 (still accepting T. exsulans as its synonym) as a junior synonym of Tritonia tetraquetra (Pallas, 1788). However, recently Korshunova & Martynov (2020) employed molecular analysis to determine that Tritonia exsulans is not a synonym of Tritonia diomedea but a valid species. After years of confusion, three species are now recognized in this complex: Tritonia tetraquetra and Tritonia exsulans, and Tochuina gigantea (Bergh, 1904).

Tritonia exsulans' body typically light pinkish to dark salmon with a white line marking the edge of the dorsum, the foot margin and the oral veil. The indistinct notal edge has about 30 distinct, branched dorsolateral processes. The bilobed oral veil bears 10-30 white digitiform processes.

Its current geographical range is Aleutian Islands, Alaska to La Jolla, California; Central Gulf of California; and Panama, where it has been observed to feed on sea pens and sea whips. Specimens may reach 300mm in length, occurring at depths from 5-100 meters depth.


Korshunova, T.; Martynov, A. 2020. Consolidated data on the phylogeny and evolution of the family Tritoniidae (Gastropoda: Nudibranchia) contribute to genera reassessment and clarify the taxonomic status of the neuroscience models Tritonia and Tochuina. PLOS ONE. 15(11): e0242103.

Martynov A.V. 2006. Nudipleura. In: Yu. I. Kantor & A.V. Sysoev (eds.), Marine and Brackish Water Gastropoda of Russia and Adjacent Countries: An Illustrated Catalogue. Moscow, KMK Scientific Press, pp.267-294.

Martynov AV. 2009. Opisthobranch mollusca of Russia: the neglected diversity of cold waters. Western Society of Malacologists, Annual Report 39: 22-23.

Dave Behrens
Sammamish, WA 98074
Feb., 2022
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Kevin at left with lifeguard Carter and Craig at right

"...Rough winds whipped down the canyon in Malibu, as I dodged fallen road signs and large trees (being cut up by firemen), enroute to Pt. Dume. On arrival, I noticed motor scooters and heavy trash cans were blown over. My buddy, Craig Hoover, joined and we geared up in a minor sandstorm. The beach drop off is quick and deep, more dicey than Vet's, but we had no issue entering the ocean. It felt good to submerge in calm waters. Viz was 15-20. Our mission was to find Tritonia exsulans, but we were foiled and forced to call the dive after 30mins, due to photo equipment issues (one of Craig's strobes was exhaling bubbles).

Fortunately we had both toted 2 tanks each, so we geared up for a second try and plunged back into the water. Shazam! Craig, normally a rather sedate person, was dancing a jig underwater. He found a T. exsulans, a big one, laying eggs! In that area we found about 7 altogether. Being my first encounter with the beast, the dive rated "excellent". Craig was doing a slug survey and we ended up with 11 species. T. exulans is the former T. diomedea (not sure when the name changed). It primarily feeds on sea pens.

My second dive exit was rather ungraceful and, for the second time in my dive history, I got unceremoniously rolled by a wave (the berm is very abrupt and I was on top of it with my fins on, before I knew it and got knocked down by hefty backwash). I started the noble, er, ignoble crawl up the beach to be pushed back halfway, with each incoming wave backwash. Fortunately an alert lifeguard, Carter, lent a kind hand and plucked me from the drink.

Pt. Dume is an historical place, important to boat navigation for centuries. And, it's a very popular spot for rock climbers to test their mettle.

On arriving home, it took hours of rinsing and blowing to rid my equipment of pesky sand, not only from the ocean but also airborne..."

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