A sea slug no bigger than a sesame seed has turned up in the waters off Taiwan, and it is the first new species in its genus to be named in 30 years. The animal, covered in black and yellow spots that reminded scientists of scattered sesame seeds, belongs to the genus Thecacera. Researchers have named it Thecacera sesama.
A speck of a creature that took three decades to find
The slug measures only a few millimeters long. It was discovered by a team of researchers from Taiwan and Hong Kong who were surveying marine life along Taiwan's northern coast. The scientists collected specimens from shallow rocky reefs where the slugs were feeding on bryozoans, tiny colonial animals that grow on hard surfaces.
This find is significant because no new species in the genus Thecacera had been formally described since the mid 1990s. The genus itself is small and rarely encountered. The discovery suggests that more tiny, overlooked species may be hiding in plain sight along well studied coastlines.
Why local divers and scientists took notice
For local marine biologists in Taiwan, the find highlights how much remains unknown about the island's underwater biodiversity. Taiwan sits at a crossroads of tropical and temperate marine ecosystems, making it a hotspot for small, cryptic species. Divers and researchers who frequent the northern reefs had not previously spotted this slug, likely because of its tiny size and camouflage.
The species name sesama comes from the Latin word for sesame, a nod to the pattern of dark spots on its pale body. The researchers published their findings in the journal ZooKeys, noting that the slug's anatomy and genetic makeup set it apart from other members of its genus.
A reminder of what still hides in shallow water
The discovery of Thecacera sesama shows that even in relatively accessible habitats like shallow reefs near a major city, new species can emerge. The slug was found in waters that are regularly visited by recreational divers and researchers. Its existence went unnoticed until a dedicated survey turned over the right rock, literally.
This find does not rewrite the textbooks on marine evolution, but it does underscore how patient field work can still yield surprises. For a genus that had gone three decades without a new addition, this tiny slug is a quiet signal that the ocean floor still holds secrets worth looking for.
