Just three millimeters long, the new species of Thecacera discovered in Taiwan feeds on a bryozoan that could prove to be another discovery

A discovery made by chance, on a millimetre scale, highlights the extraordinary ecological variety of the Taiwan seabedThe identification of Thecacera sesame It offers a valuable missing piece in the study of the micro-ecosystems of the Western Pacific, confirming how biological research finds valuable allies even in amateur explorations. The identification of this tiny sea snail, characterized by a translucent body speckled with yellow and black, adds a new and fascinating chapter to the biodiversity map in an area already considered a global biological hotspot.

A sea snail the size of a sesame seed

Thecacera sesame It is a small sea snail with a translucent white body covered in dense black and yellow dots and white snowflake-shaped spots. Researchers from the National Taiwan Ocean University, the National Museum of Natural Science, and the National Taipei University of Education have named it "fellow”, because the spots that dot the dorsal surface of the species are reminiscent small sesame seeds. And also because this new species of nudibranch, whose scientific description has just been published, has a just three millimeters long – like a small sesame seed, or a kiwi seed.

“Taiwanese divers call it 'sesame' in Chinese and it is also as small as a sesame seed, hence the name,”

explains the research team.

It would have been easy to miss on the colorful seabed of Keelung, north of Taiwan. Yet it was discovered completely by chance:

“During a recreational dive in the summer of 2019, while he was a college student, Ho-Yeung Chan accidentally discovered Thecacera sesama sp. nov. in the waters of northern Taiwan,”

The researchers explain. Chan, one of the authors of the study, realized it was a previously unknown species only after consulting a nudibranch expert.

Biology, behavior and interaction with the habitat

The classification of the Thecacera sesame as a new species was possible thanks to the combination of traditional morphological examination with the molecular phylogenetics. While sharing a similar spotted coloration to that of Thecacera pennigera, the new species is clearly distinguished by its significantly smaller body size.

Researchers have discovered that it is the “sister species” of the Thecacera picta, another small sea snail characterized by brightly colored spots. Like the latter, the Thecacera sesame interacts with a particular species of bryozoan, a sessile colonial organism known for creating fouling on ship hulls.

The four main behaviors observed – feeding, foraging, mating and egg-laying – occur in the vicinity of the bryozoan coloniesAs the study states,

“Specimens are typically found in close association with their bryozoan prey, often positioned above or immediately adjacent to active colonies.”

The sea snail is a highly specialized predator that feeds on a certain species of bryozoan. The most fascinating fact is that this bryozoan does not resemble any of those already identified as prey of other species of Thecacera. The observation of the Thecacera sesameIn short, could bring with it the discovery of a new species of Bryozoa.

The importance of a discovery that occurred by chance

Although it happened by chance, the discovery of the new species Thecacera sesame has an extraordinary importance. First of all, it is the first formal description of a member of the genus Thecacera in almost thirty yearsAnd it happened in a region where nudibranch diving is only possible for four months of the year due to seasonal typhoons, waves, and prohibitive temperatures.

The Western Pacific region where the sighting occurred is also considered a biodiversity hotspot Marine life: According to the IOC Western Pacific Subcommission (WESTPAC), the area is home to over 75 percent of all known coral species, 50 percent of the world's coral reefs, the largest area of ​​mangrove forests, and 3.000 fish species.

“The Western Pacific region, including the waters around Taiwan, represents a biodiversity hotspot for marine gastropods, yet the nudibranch fauna of this region remains poorly documented compared to other marine biogeographic provinces,”

scientists explain. There could be many other species still to be discovered in Taiwanese waters. As the study states,

“This discovery highlights the rich, yet poorly documented, marine biodiversity of Taiwan and underscores the importance of combining traditional morphological examination with molecular phylogenetics for accurate species delineation in cryptic nudibranch lineages.”

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