Ndibranch experts reveal that the sea slug Trinchesia caerulea – first described in 1804 – is actually four different species, three of which are new.

Divers searched for what were thought of as Trinchesia caerulea around Europe – in the UK, Ireland, Norway, Sweden, Spain, Italy, France, Croatia and Russia. Even though the European nudibranch fauna is one of the best studied in the world, after detailed analysis of the specimens the scientists declared three new species.

Trinchesia cuanensis nudibranch
Trinchesia cuanensis nudibranch by Tim Nicholson. Taken on Garden Rock, Isle of Man.

The new species have been named Trinchesia cuarensis, Trinchesia diljuvia and Trinchesia morrowae.

Trinchesia cuanensis has so far only been found in the UK, Ireland and Sweden. T. diljuvia appears to be is unique to the Black Sea whilst the third new species, T. morrowae, lives in the Mediterranean.

Look for the Trinchesia cuanensis nudibranch at depths of between 10 and 20 m in stony areas. Occasionally you might see one at just 1 or 2 metres. The animal grows to 15 mm long and has up to ten rows of cerrata (the projections along its back). These cerrata have a band of orange or yellow at the top, preceded by a blue band. You can tell T. Cuanensis from T. caerulea by the third band of colour at the base of the cerrata. In T. cuanensis it is dark grey or black whilst in T. caerulea it is much paler.

The new northern species was named after Lough Cuan, an alternative name for Strangford Lough in Northern Ireland, where many marine biological studies have been undertaken over the past 100 years.

Animalia (Kingdom) > Mollusca (Phylum) > Gastropoda (Class) > Opisthobranchia (Subclass) > Nudibranchia (Order) > Trinchesiidae (Family) > Trinchesia (Genus)

Further Reading

Multilevel fine-scale diversity challenges the ‘cryptic species’ concept.
Tatiana Korshunova et al. Scientific Reports 9, Article number: 6732 (2019)

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