A sea slug smaller than a sesame seed has turned up in Taiwan's coastal waters, and it is so tiny and unusual that scientists realized they had discovered a completely new species. The translucent nudibranch, named Thecacera sesama after its black-and-yellow sesame like appearance, measures less than three millimeters in length. It was first spotted during a casual dive and later identified with help from a sea slug expert on Facebook.
A chance dive and a Facebook consultation led to the discovery
Lead author Ho-Yeung Chan was an undergraduate student in 2019 when he accidentally found the creature during a recreational dive off the coast of Keelung in northern Taiwan. At first, Chan did not realize he had stumbled upon a species unknown to science. The breakthrough came after he contacted a sea slug expert online. According to the research team from National Taiwan Ocean University, the National Museum of Natural Science, and National Taipei University of Education, Chan never realized Thecacera sesama was a new species until he consulted the sea slug expert Hsini Lin teacher on Facebook.
Harsh weather made studying the tiny slug a challenge
Researching the species proved difficult because of unpredictable conditions along Taiwan's northern coastline. Strong seasonal weather patterns greatly limit opportunities for underwater surveys. Taiwan regularly experiences typhoons during the summer, while winter monsoon seasons bring large waves and colder waters. Sea temperatures can drop below 16 degrees Celsius, making diving conditions difficult for much of the year. Because of this, researchers are only able to conduct nudibranch studies for roughly four months annually. The scientists noted that locating such tiny marine animals often depends heavily on luck due to their size and the limited research window.
The slug's simple life and hidden habitat
Researchers observed that T. sesama appears to spend its life focused on just four main activities: feeding, searching, mating, and laying eggs. The species was found living on bryozoans, tiny aquatic invertebrates commonly known as moss animals. Interestingly, the bryozoan species serving as the sea slug's habitat may itself be previously unknown to science. Taiwanese divers call the slug sesame in Chinese, and it is also small like a sesame seed, hence the name.
Nudibranchs, despite their small size, play an important role in marine ecosystems. The discovery of Thecacera sesama in Taiwan's waters highlights how many hidden ocean species may still be waiting to be found, even in areas where people regularly dive.
