Long-cerata Sea Slug

Tergiposacca longicerata is one of the most scientifically remarkable nudibranchs in the Indo-Pacific. It is the type species of the genus Tergiposacca — a genus established only in 2016 by Cella, Carmona, Ekimova, Chichvarkhin, Schepetov and Gosliner in their landmark molecular phylogeny of the family Fionidae. Finding this species on a dive is an extraordinary scientific event. Each documented sighting contributes directly to our understanding of this almost unknown animal. Encountering it at our macro photography dive sites in Romblon represents a genuinely rare privilege.

Appearance and Identification

Tergiposacca longicerata displays a translucent, elongate body. Red jaws are clearly visible through the skin — a distinctive field mark. The rhinophores and oral tentacles are smooth and relatively short. The cerata are numerous, long, relatively thick and of constant diameter along their length. Some cerata show a slight swelling in the upper tenth. The digestive gland is visible through the skin. The cnidosac is translucent with an opaque white ring around the ceratal apex. This combination of features makes it unlike any other aeolid nudibranch in the region.

Scientific Significance

Tergiposacca longicerata is the sole species in its genus. The 2016 paper that described it fundamentally reorganised the family Fionidae using molecular phylogenetics — combining mitochondrial and nuclear gene sequences — and proposed sweeping changes to nudibranch classification at family and genus level. Furthermore, the genus name Tergiposacca reflects its dual character: the body plan resembles Tergipes, while the saccate egg mass form distinguishes it clearly. This species is documented from the Indo-Pacific, including the Philippines. Its presence in Romblon adds it to the growing list of scientifically significant macro subjects documented in our Marine Life Encyclopedia.

Diving with Tergiposacca longicerata in Romblon

This species inhabits silty substrate at depth — typically around 20 metres — making it well within recreational diving range at our sites around Alad Island. Our SDI/TDI trained guides actively search for rare aeolid nudibranchs on every macro dive. Photographing Tergiposacca longicerata contributes genuine data to science. Submit your sighting to the iNaturalist taxon page and help researchers map its distribution across the Indo-Pacific. For taxonomy, visit the WoRMS species page.