Trinchesia caerulea

Trinchesia caerulea (Montagu, 1804)

Taxonomic note: The phylogenetic analyses performed by Cella et al. (2016) revealed that the traditional Tergipedidae family is polyphyletic and belongs to a larger monophyletic clade including members of the traditional families Eubranchidae, Fionidae and Calmidae; this was an unexpected result, since the validity of these taxa and their distinctness from the Tergipedidae was never questioned before. They proposed to join the families Tergipedidae, Eubranchidae, Calmidae and Fionidae under the name of Fionidae. Within Fionidae, obtained results demonstrated the need of developing a new classification as previous classifications (for instance, separating Catriona, Cuthona and Trinchesia as distinct taxa) were inconsistent with the resulting phylogeny. Analyses also recover a clade (Tenellia) that includes all members of the genera Tenellia, Trinchesia, Phestilla, Catriona and the majority of described and undescribed Cuthona species. New genera Rubramoena, Abronica and Tergiposacca are proposed to group other species. This molecular study also suggests that Fionidae is rich in cryptic species complexes, difficult to separate by traditional taxonomic characters, and a great previously undetected species diversity.
A few months later Korshunova et al. (2017) take up the study of the phylogeny of the Tergipedidae and using not only molecular data but also morphological and ontogenetic data they severely criticise the work by Cella et al. (2016), proposing to reinstate the families Calmidae, Eubranchidae, Fionidae, Tergipedidae, Cuthonidae, Cuthonellidae and Trinchesiidae, the latter being the most abundant in specific taxa. They also reinstate the genera Catriona, Diaphoreolis, Phestilla and Trinchesia that in the paper by Cella et al. (2016) had been included in the genus Tenellia. Korshunova et al. also describe a new genus, Zelentia that includes Z. pustulata (type species Eolis pustulataAlder & Hancock, 1854), Z. fulgens (MacFarland, 1966) and a new species from the Barents Sea, Z. ninel, indicating important p-distances among the three species (between 10.49% and 13.83%). All previous genera, Korshunova et al. (2017) consider them within the family Trinchesiidae. They also question the validity of the Rubramoena genus of Cella et al.
The position of WoRMS is conservative, maintaining the families Cuthonidae, Calmidae, Cuthonellidae, Eubranchidae, Fionidae, Pseudovermidae, Tergipedidae and Trinchesiidae within the superfamily Fionoidea. The European species that, until recently, were considered as Cuthona, WoRMS considers them within the genus Trinchesia, as T.albopunctata, T.caerulea, T.foliata, T.genovae, T.granosa, T.ilonae, T.miniostriata and T.ocellata. Rubramoena is also considered a valid genus in WoRMS. These opinions are those that we accept in OPK while no other more conclusive data are available.

• Doris caerulea Montagu, 1804
• Eolidia bassi Vérany, 1846
• Eolis deaurata Dalyell, 1853
• Eolis glotensis Alder & Hancock, 1846
• Eolis molios Herdman, 1881
• Cuthona caerulea (Montagu, 1804)
• Tenellia caerulea (Montagu, 1804)

Description
The size of this species can reach up to 25 mm in length, although it uses to be smaller, of about 10-12 mm in length. The body background color is whitish but has a very soft yellowish green hue in some areas. Oral palps and rhinophores are relatively short and colored whitish yellow at the base and orange at the tips. The rhinophores are very close together at the base and the eyes are located slightly behind and outside of the base of the rhinophores. The cerata are short and fusiform and gathered in 6-7 groups at each side of the body with up to 3 ceratas each. Between the first and second group of cerata, in the center of the back, there is the cardiac area. The color of the cerata makes this species unmistakable: the translucent base with some tiny blue spots, then a dark blue ring (that gives its name to the species), then an orange ring and finally the translucent apex. With all this coloration of the cerata, the dark digestive gland running inside is barely visible. The foot is narrow and translucent white. Can be confused with Trinchesia morrowae.

Biology
T. caerulea is one of the most common nudibranchs on rocky shores, generally with little illumination and abundance of algae and hydroids. Among hydrarians on which it has been cited we can be highlight Aglaophenia pluma, Eudendrium racemosum, Halecium halecinum and different species of Sertularella (S.polyzonias, S.crassicaulis, S.gayi), on which it feeds. The spawn is laid on the hydrarian the animal feeds on, wound into a flat spiral of about 2 and a half turns filled with white oval eggs, helically arranged within the cord; the size of the eggs is about 200 microns.

Etymology

• Trinchesia. In honor of Professor Salvatore Trinchese (1836-1897), Italian opisthobranchiologist, Professor of Zoology at Bologna University and successor of Paolo Panceri as Professor of Comparative Anatomy at the University of Napoli.
• Caerulea means “sky blue, esp. the deep blue of a Mediterranean sky at Mid-day” according to Bernard Picton at Nudibranchs of the British Isles

Distribution
This species inhabits European Atlantic waters from Ireland and the British Isles, the Açores and the Canary islands. It is also present in the Mediterranean, where it is mainly found in the western basin. Although it is cited in Greece (Koukouras, 2010), we did not find any information that allows us to confirm this identification. In the Iberian Peninsula it is found in all coastal areas, including Portugal. It has also been cited in Balearic islands. In the Catalan coast it has been observed in many localities of the Costa Brava, from the Port de la Selva to Blanes.

Similar species
Trinchesia morrowae, smaller, with a white mid-dorsal band, cerata with a ring of yellow or golden dots below the blue band. Oral tentacles and rhinophores with orange tips, not yellow. Trinchesia cuanensis, cerata with dark brown or black base, with a band of yellow dots under the blue band but without the white mid-dorsal band.

More pictures

Trinchesia caerulea by Enric Madrenas

Trinchesia caerulea by Enric Madrenas

Trinchesia caerulea by Enric Madrenas

Trinchesia caerulea by Enric Madrenas

Trinchesia caerulea @ Croatia by Djani Iglic

Trinchesia caerulea @ Croatia by Djani Iglic

Trinchesia caerulea @ Croatia by Djani Iglic

Trinchesia caerulea by Miquel Pontes

Trinchesia caerulea @ France by Pascal Girard

Trinchesia caerulea with no blue rings @ France by Pascal Girard

Trinchesia caerulea by Manuel Ballesteros

Bibliography

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Bibliography based on the works by Steve Long, 2006. Bibliography of Opisthobranchia 1554-2000 and Gary McDonald, 2009. Bibliographia Nudibranchia, with later updates from other resources.

Further reading

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