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Circus Sea Slugs: How clown nudibranchs are like real-life Pokémon

April 17, 2026

The Pokémon “Shellos” and its evolution “Gastrodon” (whose pink West Sea variant is one of my favorite Pokémon) resemble a sea slug. Don’t just take my word for it, though—in their Pokédex entries, Shellos and Gastrodon are referred to as the “Sea Slug Pokémon”. The Pokémon Goomy is referred to as a Mollusk Pokémon in many languages, and although sea slugs are a type of mollusk, the resemblance is less apparent. The team behind the games really didn’t have to change much from their real-life inspiration, though, as sea slugs are some of the most unreal-looking creatures in our oceans. As Helen Sullivan writes about sea slugs, which are also known as nudibranchs, in the Smithsonian Magazine, “It is really, really difficult not to compare them to Pokémon characters” (2024).

Nudibranchs belong to the class Gastropoda, which falls under the phylum Mollusca (mollusks). The term sea slug is used to broadly refer to 11 different subgroups under Gastropoda that do not have hard outer shells. True nudibranchs account for only one of these subgroups, but the others are sometimes also referred to as nudibranchs for convenience (Davey & Willan, 2020). 

When reading about species of nudibranch, one caught my eye for its name and bright orange coloration: the clown nudibranch. Even the name makes them sound like some sort of Pokémon! They are quite small—around 3 cm on average for adults—but their orange spots would probably make them hard to miss. The name, appearance, and distinctive characteristics of this creature gave me the idea to make a faux Pokémon card for the species, whose scientific name is Ceratosoma amoenum.

Illustration/Graphic Design by Priyanka Singh

Dorid

Nudibranchs can have a few different body plans that differ in shape, gills, and more. C. amoenum has a dorid nudibranch body plan, which means it has two protrusions on its front end and a bundle of protrusions on its back end. The two protrusions that resemble antennae are called rhinophores while the bunch of protrusions on its backside are actually its gills! This distinctive characteristic is where nudibranchs get their name from. Nudibranch means “naked gills” (Sullivan, 2024).

Not to be confused with…

When researching for this article, I found that there are other nudibranch species with a similar appearance and common name as C. amoenum. Trophia catalinae also has a white body with orange spots, although its spots are raised (known as “tubercles”), and its rhinophores and gills are orange rather than magenta. It’s referred to by a similar name: “sea clown trophia” or simply “sea clown”, so you can see where the confusion might arise. Trophia modesta is a species that was recently distinguished from Trophia catalinae in a 2020 study, and it is commonly known as the “modest clown dorid” (Jung et al.). Unsurprisingly, it looks more similar to T. catalinae than it does to C. amoenum, although its body is more translucent than T. catalinae’s. Still, an amateur nudibranch enjoyer may get these species confused at first glance.

Defensive glands

Nudibranchs often contain chemical defenses within their bodies. A protective tissue called the mantle contains glands that secrete the toxins (Davey & Willan, 2020). Like other nudibranchs, our clown friend doesn’t produce these toxins on their own—they obtain them from their diet, which consists primarily of sponges (Winters et al., 2018). This chemical defense is critical for the soft, shell-less nudibranchs.

Shell loss

Speaking of not having a shell, both the English and Japanese name for Shellos mean “lost shell”: Karanakushi in Japanese, with kara meaning “shell” and nakushi being derived from nakushite (without) or nakusu (to lose); and “shell loss” (Shellos) in English (“Shellos”, 2026). The name origin references one of the nudibranch’s most defining characteristics. Gastropods have an external shell in their larval stage, although members of order Nudibranchia lose it before they reach adulthood, with C. amoenum being no exception (Davey & Willan, 2020). 

Hermaphroditism

As members of the Gastropoda class, sea slugs are hermaphrodites. Each individual has both male and female reproductive organs. I know what you may be wondering, but no, they can’t impregnate themselves, although they often donate and receive sperm simultaneously with another individual. Some nudibranchs even shed their penises after intercourse and gain a new one soon after (Sekizama et al., 2013). Talk about freaks of nature….

I considered designing a creature based on the clown nudibranch for my fake Pokémon card, but why would I when the real thing looks like that? I’ll leave the creature designs to the Pokémon team for now. I hope you’ve come to see that sometimes reality can be stranger than the fiction it inspires, and that our world is full of amazing yet often overlooked creatures like the nudibranch.

Illustration by Priyanka Singh

References

Davey, N., Willan, R.C. (2020). Super sea slugs: a guide to the sea slugs of New Zealand. (Version 1). National Institute of Water and Atmospheric Research (NIWA). 

Gastrodon. (2026). Bulbapedia. Retrieved April 17, 2026, from https://pokemondb.net/pokedex/gastrodon 

Jung, D., Gosliner, T.M., Choi, T., Kil, H., Chichvarkhin, A., Goddard, J.H.R., Valdés, A. (2020). The return of the clown: pseudocryptic speciation in the North Pacific clown nudibranch, Triopha catalinae (Cooper, 1863) sensu lato identified by integrative taxonomic approaches. Marine Biodiversity, 50, 84. doi.org/10.1007/s12526-020-01107-2 

Sekizama, A., Seki, S., Tokuzato, M., Shiga, S., Nakashima, Y. (2013). Disposable penis and its replenishment in a simultaneous hermaphrodite. Biology Letters, 9(2). doi.org/10.1098/rsbl.2012. 1150 

Shellos. (2026). Bulbapedia. Retrieved April 17, 2026, from https://pokemondb.net/pokedex/shellos 

Sullivan, H. (2024, May). Dive Into the Exotic World of Nudibranchs, the Spectacular Slugs of the Sea. Smithsonian Magazine. www.smithsonianmag.com/science-nature/dive-exotic- world-nudibranchs-spectacular-slugs-sea-180984013/

Winters, A.E., White, A.M., Dewi, A.S., Mudianta, I.W., Wilson, N.G., Forster, L.C., Garson, M.J., Cheney, K.L. (2018). Distribution of Defensive Metabolites in Nudibranch Molluscs. Journal of Chemical Ecology, 44, 384-396. doi.org/10.1007/s10886-018-0941-5 

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  Timothy Durham was convicted of rape when a test showed his DNA genotype matched the DNA recovered from the crime scene. Eye witnesses testified that Durham was in a different state at the time of the incident, but he wasn’t exonerated from his 3000 year sentence until follow up DNA analysis showed that the preliminary forensic analysis used in the trial was misinterpreted (Thomas et al.). DNA testing serves an invaluable part in our criminal justice system, but it comes with complications and bias that can lead to wrongful convictions and misinformed juries.  

Background:

Forensic genetics aims to identify the origin of a biological sample. It can be traced back to Karl Landsteiner who discovered human ABO blood groups. With blood groups, suspects could be eliminated based on their blood type. For example, if a suspect had type A blood and there was type B blood left at the scene by the perpetrator, the investigators could rule out the suspect. Unfortunately, the reverse didn’t work. If the suspect and perpetrator both had the same blood type, it can’t be concluded that the suspect was guilty. Blood identifiers evolved into 8 distinct categories which improved the ability to eliminate suspects, but could only conclude that (if the system matched) it might be the perpetrator or this person might be related to the perpetrator (Jobling and Gill). The field evolved in the 1980s with the discovery of Minisatellites, lines of repetitive DNA that don’t encode proteins. Minisatellite patterns in DNA create what we know today as the DNA fingerprint, and it has a much higher accuracy rate than previous methods (Augustyn et al.). Around the same time, a breakthrough for victims of sexual assault was discovered. In the case of assault, bodily fluids of both the victim and the assaulter can get mixed. A process called differential lysis was created which could selectively increase the concentration of sperm in a fluid sample thereby allowing for accurate DNA testing (Jobling and Gill). Forensics evolved to use single-locus probe testing after several years because of its ease of interpretation. It looked at specific minisatellites that had high variability between subjects. This was the first DNA-based method to be used in a criminal investigation. Two murder homicides from several years apart were connected using DNA evidence. The evidence was then used to exonerate an innocent man, and the guilty party was found when he tried to evade mandatory DNA testing for all men in the small town. His guilt was then reinforced when the DNA profiles matched, and he gave a confession (Jobling and Gill). Finding DNA at a crime scene doesn’t guarantee that you’ll find a murderer. There are issues with non-pure samples and limited samples that make DNA work difficult, and accreditation of facilities and new techniques and take time (Jobling and Gill).  

Subjectivity of DNA Interpretation:

In a 2009 publication, the National Academy of Science discusses the possibility for subjective influence in lab based forensics. The interpretation bias happens in complex cases where, for example, there could be a mixture of DNA. A study published in 2011 looked specifically at this issue. A gang rape happened in Georgia, and the mixture in DNA from the case was used to prosecute one suspect after another suspect took a plea bargain to testify against him. With DNA mixtures, there are three possible conclusions: suspect excluded, suspect cannot be excluded, and inconclusive. If the suspect is excluded, it means that there’s little to no possibility that his DNA is part of the sample. If the suspect cannot be excluded, it means that there’s a possibility that his DNA is part of the sample. In the trial, the DNA examiners who knew the context of the case concluded that the suspect being prosecuted could not be excluded. The 2011 study gave the DNA evidence from this case and the DNA profiles of the suspects to 17 forensic examiners. These examiners had no context of the case, and they all worked independently. Of the 17, only 1 came to the same conclusion (suspect cannot be excluded) as the examiners who knew the context of the case. Twelve of the 17 concluded that the suspect who was prosecuted and convicted had no relation to the DNA found in the sample. Not only does this show that subjectivity occurs due to the context of the case, but the 17 examiners came up with different findings based on their past experiences meaning that not all DNA analysis is objective. Some organizations like the Scientific Working Group on DNA Analysis Methods say that quantitative statistical evidence should be presented with every categorical conclusion, but the US doesn’t require this (Dror and Hampikian).

False Positives:

There are two categories that cause wrongful identification in a DNA report: coincidental matches and false positives. Coincidental matches are DNA matches between two unrelated people. The probability of these matches is about 1 to 500,000 for white individuals and about 1 to 350,000 for black individuals. This small probability of coincidental matches makes people feel confident in DNA evidence. False positives, on the other hand, are matches between DNA and test DNA that result from issues in the forensics lab. There have been multiple cases of forensics labs accidentally switching victim and suspected rapist DNA which lead to convictions that were later overturned when the lab realized the error. There are also cases of misreading or misunderstanding a sample. In a case from 1993, a man was convicted of rape because someone interpreted a mixed sample of victim and perpetrator DNA as an individual sample. The conviction was again overturned. To prevent false convictions, retesting DNA is allowed, but it’s not an efficient solution. Many people are pushing for statistical information on the probability of false positives, so that the jurors can make accurate judgements based on DNA evidence (Thomas et al.).  

Conclusion:

DNA analysis is a useful tool for the criminal justice system, but subjectivity can be an issue in forensic testing. To combat wrongful convictions, there are organizations like The Innocence Project who use DNA testing to free the innocent, but reformed forensic testing standards should be put in place to prevent subjectivity and to ensure juries are correctly informed during trials. https://www.innocenceproject.org/    

Citation:

Augustyn , Adam, et al. “DNA Finerprinting.” Encyclopedia Britannica , 26 Apr. 2018, www.britannica.com/science/DNA-fingerprinting#ref153186. Dror, Itiel E., and Greg Hampikian. “Subjectivity and Bias in Forensic DNA Mixture Interpretation.” Science & Justice, vol. 51, no. 4, 2011, pp. 204–208., doi:10.1016/j.scijus.2011.08.004. Jobling, Mark A., and Peter Gill. “Encoded Evidence: DNA in Forensic Analysis.” Nature Reviews: Genetics, vol. 5, no. 10, Oct. 2004, pp. 739–751., doi:10.1038/nrg1455. Thompson, William C, et al. “How the Probability of a False Positive Affects the Value of DNA Evidence.” Journal of Forensic Sciences, vol. 48, no. 1, Jan. 2003, pp. 1–8., doi:10.1520/jfs2001171.