Tethys fimbria is a fascinating species of predatory sea slug, known as a nudibranch, which inhabits the Mediterranean Sea and the eastern Atlantic Ocean. Recognized as a valid name by the International Commission on Zoological Nomenclature, Tethys fimbria is synonymous with Tethys leporina Linnaeus, 1758. This species stands out as the only member of the genus Tethys, under the family Tethydidae.
Identifying Tethys fimbria is straightforward due to its distinctive physical features. This nudibranch can grow up to 30 cm in length. It possesses a large and broad oral hood at the front, fringed with sensitive papillae, which is used to capture food. The rhinophores are small and mainly hidden within the expanded collar of the sheath that encircles them. The body is translucent white with blackish brown spots on the cerata and occasionally on the edge of the oral hood and foot. The cerata, large and flattened, are easily autotomised as a defense mechanism.
Tethys fimbria is notable for its unique characteristics. It lacks a radula, unlike many other nudibranchs. The cerata, which can be self-amputated when the slug is threatened, are smooth and adorned with blackish brown spots. The species also produces large amounts of prostaglandins within its mantle, which are subsequently moved to the cerata. This nudibranch is also a proficient swimmer, using its body undulations for locomotion.
The preferred habitat of Tethys fimbria is soft sandy-mud substrates, at depths ranging from 20 to 150 meters. It feeds on small crustaceans, using its broad oral hood to effectively capture prey. These nudibranchs are typically found in deeper waters, often hidden among the sandy and muddy bottoms where they can camouflage effectively.
An intriguing aspect of Tethys fimbria is its ability to autotomize its cerata. When threatened, this nudibranch can self-amputate its cerata to distract predators, allowing it to escape. Additionally, the production and transfer of prostaglandins to the cerata is a unique biochemical trait, playing a role in the nudibranch’s defense mechanisms.
Scuba Diving Gozo in Malta offers excellent diving spots to observe Tethys fimbria in its natural habitat. Some of the best locations to see these remarkable nudibranchs include:
Il-Kantra, Gozo’s South Coast – This site provides an ideal environment for Tethys fimbria, particularly at depths around 30 meters where they are commonly found.
Cirkewwa – On Malta’s northern tip, known for its clear waters and diverse marine life, making it an excellent spot to encounter Tethys fimbria.
Hondoq Bay – Situated on Gozo’s southeast coast, this area offers rocky substrates and sandy-mud bottoms, attracting these unique sea slugs.
Diving at these locations, particularly at deeper depths where Tethys fimbria thrives, provides an exceptional opportunity to observe and photograph these fascinating creatures in their natural setting.
