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Posts tagged ‘opalescent nudibranch’

Opalescent Nudibranch – 3 Distinct “Hermissenda” Species in the North Pacific Ocean.

As a result of making the following post on social media, I learned that there has been a change in classifying the “Opalescent Nudibranch”.

It was Robin Agarwal who educated me and shared the following incredible photo from Monterey, California.

As you can see, the species on the left is more similar to the one I posted and which we call the “Opalescent Nudibranch” in British Columbia.

However, it has been determined (2016) that there are 3 species in the “Hermissenda” genus (all are up to about 9 cm long). One is found in the Northwest Pacific Ocean from Japan to the Russian Far East so there is no worry about confusing that one on our coast.  But, for the other two species, their range overlaps in Northern California where Robin took the photo.

 

This has of course led to the need for two common names to differentiate them there. The species on the right is being referenced as the “Opalescent Nudibranch” (reinstating the species name Hermissenda opalescens). The one on the left has retained the name Hermissenda crassicornis and is being referenced as the “Thick-Horned Nudibranch” where the species ranges overlap.

However, off British Columbia’s coast we are only likely to see the species on the left with its range being from Alaska to Northern California. Thereby, I anticipate this beautiful species will keep on being referenced as the “Opalescent Nudibranch” in the vernacular.

What are the differences between these two species?  I am so glad you asked as I totally nerded out and made a summary table to differentiate the 3 species reported in the research “The Model Organism Hermissenda crassicornis (Gastropoda: Heterobranchia) Is a Species Complex“.

The table is just for you my fellow nudibranch nerds.

But, I’ll cut to the conclusion. Don’t be fooled by the colour of the two species found in the Northeast Pacific Ocean. The colour of the cerata in BOTH species can vary from light brown to dark brown to bright orange. Cerata are the structures on some sea slugs species’ backs that have both a respiratory and defence function. The tips contain the stinging cells (nematocysts) of the nudibranch’s prey e.g. hydroids.

The easy way to differentiate the two Hermissenda species in the Northeast Pacific Ocean, is to look for white lines on the cerata. The species most often found off the BC Coast has white lines. The other does not. See my photo below to note this easily identifiable feature (and, if you need some amusement, have a look for the little hermit crab).

 

And now, for that summary table I promised you.

Then, more photos of the beautiful Hermissenda species found off our coast – Hermissenda crassicornis.

I share these to show the variation of colour in the species  but also, because by any name and classification, there can never be enough photos of such a stunning ambassador for the colour and biodiversity found in these cold, dark seas.

Source of table information and photos: Lindsay, T., & Valdés, Á. (2016). The Model Organism Hermissenda crassicornis (Gastropoda: Heterobranchia) Is a Species Complex. PLoS ONE, 11(4), e0154265. http://doi.org/10.1371/journal.pone.0154265. Click to enlarge.

 

See my previous blog at the link for “Attack of the Sea Slugs” in which one Opalescent Nudibranch attacks another.

 

Feeding on Orange Hydroids. ©Jackie Hildering.

Hermissensa crassicornis feeding on Bushy Pink-Mouth Hydroids. Red-Gilled Nudibranch also snacking away in the background.©Jackie Hildering.

Hermissensa crassicornis on Eel Grass. ©Jackie Hildering.

With a “Jointed Three-Section Tubeworm”. ©Jackie Hildering.

Feeding on hydroids, Red Soft Corals to the left and crawling on a Red Ascidian (highly advanced invertebrate, the most advanced of all in the image). ©Jackie Hildering.

Hermissensa crassicornis feeding on Pink-Mouth Hydroids. Here you can very clearly see the distinctive white lines on the cerata. ©Jackie Hildering.

Hermissensa crassicornis on Bull Kelp. Hooded Nudibranchs in the background. ©Jackie Hildering.

On Red Soft Coral. ©Jackie Hildering.

Hermissensa crassicornis on Solitary Pink-Mouth Hydroid. ©Jackie Hildering

Hermissensa crassicornis egg mass. ©Jackie Hildering

Attack of the Sea Slugs!

[Update March 2018 – There has been a reclassification of this species of nudibranch whereby Hermissenda crassicornis  is also being referenced as the “Thick-Horned Nudibranch. Please see my blog at this link for that information.]

This is an Opalescent Nudibranch (Hermissenda crassicornis).

Opalescent nudibranch. The white batch is a colony of animals known as kelp-encrusting bryozoan. © 2014 Jackie Hildering; www.themarinedetective.ca

Opalescent nudibranch – species up to 8 cm long. The white patch on the right is a colony of animals known as “kelp-encrusting bryozoan”. © 2014 Jackie Hildering; http://www.themarinedetective.ca

Here is one climbing giant kelp with hooded nudibranchs in the background.

Opalescent nudibranch © 2014 Jackie Hildering; www.themarinedetective.ca

   © 2014 Jackie Hildering; http://www.themarinedetective.ca

I know! Aren’t they astonishingly beautiful? Opalescent Nudibranchs are one of the most powerful ambassadors for shattering the misconception that warm waters are home to more colourful life. They truly help in raising awareness about the incredibly exotic and vibrant life hidden just below the surface in the dark, rich, cold waters of the NE Pacific.

But they help with something else too.

I recently received a video clip of Opalescent Nudibranchs from Tavish Campbell, taken while with Pacific Wild documenting the life that would be at risk if tanker traffic came to Caamano Sound. Tavish, who is a fellow-diver and appreciator of all things marine, asked, “Hey Marine Detective, what’s going on here?!”  What I saw led me to realize how this species is also a very powerful engager for addressing another default notion we humans seem to have.

We tend to bestow judgemental labels on animals depending on our interpretation of their beauty.  We are inclined to think beautiful animals are “nice”, “cute” and “benign”, and foreign looking animals are “mean”, “ugly” and/or “bad”.

While I appreciate that some organisms may be more aesthetically pleasing than others, there is no “ugly” in Nature and there certainly isn’t “bad”.  Organisms look and live as they do because it works. Their appearance and behaviours are the result of expanses of time longer than we humans, as newcomers, can truly appreciate. Organisms’ adaptation allow them to survive and fulfil their niche in Nature’s puzzle so that there is the greatest chance of balance. [Insert “God” instead of “Nature” if this is your preference.]

Therefore, for example, there are no “bad” kinds of orca but rather orca populations whose job in Nature is to eat other marine mammals. There are dolphins that sometimes kill other marine mammals without this being for the purposes of food (no matter how much this conflicts with the “Flipper-like” identities we have imposed on them). Sea otters do things that definitely are NOT cute and .  . . it also means that beautiful sea slugs will also do what they need to in order to survive.

I take such comfort in not needing to judge Nature. It just is. In contrast, human behaviours too often do NOT enhance the potential of balance in Nature or even the chances of our own survival.

So here’s the jaw-dropping video. Ready . . .?

Opalescent Nudibranchs in all their beauty, are extremely voracious predators and, as is evident in the video, will also attack their own kind. Reportedly, fights most often result when the animals come into contact head-to-head. The animal closest to the head or end of the other has the advantage of getting in the first bite and thereby the greater likelihood of killing their opponent and eating them.

But, they are hermaphrodites, they need one another to mate! As hermaphrodites, there is not even male-to-male competition for females! So why, when your chances of finding a mate as a sea slug are already pretty limited, would you kill another of your kind instead of mating with them?

I hypothesize that it would have to do with the balance between needing to eat and needing to mate and/or that there is some sort of genetic competition going on. That’s all I got. Insert rap awe and wonder here. I may not know why they do what they do but I do know, there has to be an advantage to their survival.

What I also know for sure is that this gives a whole new meaning to “slugging it out”!

Opalescent nudibranch egg mass. http://jackiehildering.smugmug.com/Underwater/Sea-slugs/

Opalescent Nudibranch egg mass. Every species of nudibranch has distinct egg masses i.e. they are species specific.  2014 Jackie Hildering; http://www.themarinedetective.ca