A Sea Slug Smaller Than a Sesame Seed Is a Brand-New Species

Some of nature’s most delightful discoveries are also among its smallest. Off the coast of Keelung in northern Taiwan, scientists have identified a new species of sea slug so tiny it is dwarfed by a grain of rice. Described on May 27, 2026, the translucent nudibranch measures less than three millimeters long and has been named Thecacera sesama, after its black-and-yellow markings that call to mind a sesame seed.

The story behind the find is as charming as the creature itself. The slug was first spotted in 2019 by Ho-Yeung Chan, then an undergraduate, during a recreational dive. Suspecting it might be something special, he sought out a sea slug expert online, and what began as a casual observation grew into a formal scientific study. Chan went on to become the lead author of the paper, which was published in the open-access journal ZooKeys, alongside colleagues from National Taiwan Ocean University, the National Museum of Natural Science, and National Taipei University of Education.

“Off the coast of Keelung in northern Taiwan, scientists have identified a new species of sea slug so tiny it is dwarfed by a grain of rice.”

Documenting the animal took patience. Local diving conditions allow only a roughly four-month window each year, with typhoons and monsoon weather closing off the rest. The little slug lives on bryozoans, tiny colonial “moss animals,” and like other nudibranchs it plays a meaningful part in the marine food web, a reminder that even the most overlooked creatures help hold an ecosystem together.

Finding and naming a new species, especially one this small, is a small triumph of curiosity and care. It shows that you do not need a deep-sea submarine or a remote frontier to add to the catalog of life; sometimes a sharp-eyed student on a weekend dive is enough. Each new name reminds us how much beauty and biodiversity still waits, quietly, in the shallows just off our shores.