For nearly 200 years, biologists felt that they had a reasonably good grasp of the nudibranch genus Thecacera. Consisting of six identified species present in marine habitats around the globe, these shell-less molluscs appeared as small as small might be, starting from round half an inch to an inch lengthy.
Then, scientists in Taiwan discovered a seventh species, one barely the dimensions of a grain of rice.
It is taken seven years from first sighting by Ho-Yeung Chan (on the time an undergraduate at Nationwide Taiwan Ocean College) for this miniature marine animal to be formally described.
I reside round 10 km (6 mi) north of the place this new species was discovered close to Keelung port, roughly a 30-minute drive from the capital metropolis Taipei.
The shoreline right here is beautiful – surf seashores, rocky coves, colourful fishing ports – with huge, deep-green mountains taking over house in each route besides eastward. There, you may solely see ocean and the horizon line, interrupted by a couple of rocky inexperienced islands within the distance.
But it surely’s additionally solely diver-friendly for round 4 months a 12 months, as a result of summer time typhoons and harmful swells. Nice for browsing, not so good for diving, not to mention discovering a well-camouflaged sea slug just some millimeters in size.
So the possibilities of a diver discovering a novel species of this dimension are fairly low. Chan reached out to a “sea slug knowledgeable” on Fb, researcher Hsini Lin, who felt that this discovery was one thing totally new within the nudibranch world.
Ho-Yeung, Chan, et al., ZooKeys (2026)
Measuring lower than 3 mm (0.12 in), this tiny, translucent sea slug with tiny black and yellow dots is now etched into the historical past books, becoming a member of its nudibranch kin and incomes its personal spot as a novel species.
And the title? Thecacera sesama – as a result of the researchers discovered that its dimension and form resembled a sesame seed.
Of the six people collected, three performed an essential function of their classification – given their dimension, their complete our bodies had for use for DNA extraction. However via this work, the researchers discovered a 14.17% genetic divergence from the closest relative, Thecacera picta.
“Morphologically, T. sesama is uniquely distinguished by its translucent white physique coated with quite a few small, spherical, black pigment spots and fewer, bigger yellow spots,” the workforce described. “The phylogenetic evaluation locations T. sesama as a sister species to T. picta.”
And this was throughout the vary that warranted its classification as a brand new species of nudibranch.
“Taiwanese divers name it ‘sesame’ in Chinese language, and additionally it is small like a sesame seed, therefore the title,” the researchers famous.
Moreover being lovely, T. sesama is mainly a sea slug on a mission, exhibiting solely 4 behaviors: feeding, looking out, mating, and laying eggs on mossy marine organisms referred to as bryozoans.
By the way, the bryozoan that T. sesama favors might also be new, with sampling returning a mere 82% match with any identified species.
Ho-Yeung, Chan, et al., ZooKeys (2026)
“Nudibranchs are one of many key gamers within the marine meals internet, the workforce mentioned. “They’re extraordinarily colourful and might be noticed on coral reef ecosystems. Nevertheless, many nudibranchs are very small in dimension and are extraordinarily troublesome to identify underwater with the bare eye.”
T. sesama is probably going simply the primary of many undiscovered sea mollusc species dwelling within the western Pacific marine waters across the island of Taiwan.
The research was revealed in ZooKeys.
Supply: National Taiwan Ocean University through EurekAlert!
Reality-checked by Mike McRae
