Six Fun Sea Slugs

When I was reviewing the post on photosynthesizing sea slugs, I realized it was my first post on animals. This is mostly because I generally find microbes, plants, and fungi more interesting, but here's another exception to that trend. And yes, you're getting more sea slugs. I like sea slugs.

I've been excited about this one for a while because I don't do a lot of animal posts, but you have to love sea slugs. I would love to share more (maybe I will at some point) because there are so many kinds of sea slugs and they are pretty amazing creatures, but let's start with these guys for now. Have you seen any of them? A few have been popular online.

Overview

- Glaucus atlanticus

- Jorunna parva

- Dirona albolineata

- Thecacera pacifica

- Cyerce nigricans

- Cyerce elegans

The picture at the top is of a Glaucus atlanticus, also known as a blue glaucus or blue dragon sea slug. Despite the name atlanticus, they can be found in the Pacific, Atlantic, and Indian oceans in mostly tropical or subtropical areas. In addition to being gorgeous, they're super cute at a maximum length of 3 cm (1.2 inches) and spend most of their time upside down on the surface of the water. They use a kind of camouflage known as countershading - their backs blend in with the sky, and their bellies blend in with the water.

However, they're also rather fearsome. They eat stinging jellies like Portuguese Man o' Wars (men of war?) and bluebottles, shuffling the stinging cells into cnidosacs in their tendril-like cerata. Fly like a butterfly, sting like a bee, I guess. These cells are still active after death, so I recommend being careful if you're on a tropical beach. Watch your step and be careful of beached blue dragons - you can still admire from a distance, just no touching.

Australia’s “blue dragons” are stunning. Australian Geographic. (2022, January 17). http://www.australiangeographic.com.au/fact-file/blue-dragon/

Blue Glaucus. Oceana. (2023, May 18). https://oceana.org/marine-life/blue-glaucus/

Jorunna parva

This image came from https://benedante.blogspot.com/2015/07/jorunna-parva-cutest-sea-slug.html

The common name for these little (up to ~2 cm) sea slugs is sea bunny, and with good reason. They're nudibranchs found in tropical areas of the Indo-Pacific ocean and are a popular subject for underwater photography. Their primary food source is algae, but they also eat sponges and absorb the toxins the sponges produce - the cute, often brightly-coloured appearance of these slugs actually signals their toxicity. They locate their food by detecting chemicals that algae produce, then scrape it off of whatever it's growing on to eat.

These slugs are more than tiny, toxic sea-bunnies. They contain a compound called Discodermolide, which is being investigated for its potential as a cancer-fighting drug (Martello, 2001). The sea bunny also accumulates chemicals from its surroundings in its tissue, making it useful for indicating water quality.

Martello, L. A., LaMarche, M. J., He, L., Beauchamp, T. J., Smith, A. B., & Horwitz, S. B. (2001). The relationship between taxol and (+)-discodermolide: Synthetic Analogs and Modeling Studies. Chemistry & Biology, 8(9), 843–855. https://doi.org/10.1016/s1074-5521(01)00055-2

Sea bunny. American Oceans. (2023, August 16). https://www.americanoceans.org/species/sea-bunny/ 

Dirona albolineata

These gorgeous slugs are also known as frosted sea slugs, and (as you might be able to guess by the image) are found on the west coast of North America, from Alaska to southern California, and the east coast of Asia in water up to 28 m deep. They are nudibranchs, or "true" sea slugs and can get up to 18 cm (~7 inches) in length, although usually they are 4-5 cm. They have clear cerata which, as you can see, are lined with white that can appear to glow. They are carnivores, mostly preying on small crustaceans and snails using their jaws to crack the shells open.

Dirona albolineata - Facts, Diet, Habitat & Pictures. Animalia. (n.d.). https://animalia.bio/dirona-albolineata 

Thecacera pacifica

These fun fellows are often nicknamed 'Pikachu nudibranch' for their striking resemblance to the iconic Pokémon character. The 1-2 cm sea slugs are native to the Indian and Pacific oceans, including the coast of Japan. Hmm...

I wasn't able to find much information on them, but like many other nudibranchs, they are rather toxic. No electric shock abilities recorded yet.

Sain, T. (2022, November 1). Pikachu nudibranch. Our Breathing Planet. https://www.ourbreathingplanet.com/pikachu-nudibranch/

Cyerce nigricans

These pinecone-y sea slugs (I literally found them by searching "pinecone sea slug" because I didn't know the scientific name) are found in the Indo-West Pacific. The cerata are easily cast when the slug is disturbed and it secretes "distasteful secretions" (Rudman, 1999) as defense mechanisms.

Rudman, W. B. (1999, July 6). The Sea Slug Forum - Cyerce nigricans. The Sea Slug Forum. http://seaslugforum.net/find/cyernigr

I'm rather frustrated because there was barely anything available about these, but Cyerce elegans are truly elegant, so I will include a picture anyways. 
There's a little bit of information in the article below, but not much.

Cyerce elegans: Elegant Butterfly Seaslug. The Three P | Underwater Macro Photography. (2021, May 18). https://the-three-p.com/cyerce-elegans-elegant-butterfly-seaslug/#

I'm sorry I wasn't able to find more information on many of these - turns out there isn't a lot of easily accessible research. However, there are many slugs in the sea and I encourage you to seek out more if you're curious. These are just a few that spoke to me.