Catriona aurantia

Catriona aurantia (Alder & Hancock, 1842)

Catriona aurantia by Klas Malmberg

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.

Schmekel & Portmann (1982) and Thompson & Brown (1984) incorrectly classed Catriona aurantia as a synonym of Catriona gymnota (Couthouy, 1838), which lives in the NW Atlantic from Cape Cod to Newfoundland. Other authors subsequently repeated this error. Molecular sequencing showed them to be distinct separate species (Korshunova et al., 2017)..

Synonyms

• Eolis aurantia Alder & Hancock, 1842
• Eolis aurantiaca Alder & Hancock, 1851
• Cuthona aurantia (Alder & Hancock, 1842)
• Trinchesia aurantia (Alder & Hancock, 1842)

Description
This species grows up to 22 mm long. Body translucent white, sometimes with an orange or pink hue, with no surface markings. Internal organs are sometimes visible by transparency. The cerata are translucent, and are arranged in up to twelve transverse rows on each side of the body with up to seven cerata per row, more swollen than in other species of the family. They often cover the sides and much of the dorsum of the body. The pink, orange brown, olive brown or maroon brown internal digestive gland can be seen inside by transparency. The distal third of each cera has a broad white band, often stained pale orange apically in adult specimens. The ceratal tip can be translucent white, but the cnidosac is barely visible. When well fed, the cerata are robust and widest in the upper half but are thinner and more linear when unfed for some time. Rhinophores are smooth and they are translucent orange-brown with no surface pigment. Eyes are small, black and internal, and they can be seen behind the base of each rhinophore. Oral tentacles are translucent white, with no pigment on the surface. The foot is broad and rounded anteriorly, with no propodial tentacles, and it tapers to a narrow posterior point. Genital opening is below the first row of cerata on the right side of the body.

Biology
Usually found in shallow exposed locations where water movement is strong. It feeds on hydroids of the genus Tubularia, especially Tubularia larynx. Individuals are usually found amongst the stems of the Tubularia and are thought to feed by eating through the stems rather than on the polyps (Picton & Morrow, 2016). The spawn mass is a colourless, transparent kidney shape, placed at the base of its food source. The veliger larvae live in the plankton for up to ten days before transforming into the adult form. They can be found all around the year, as there are several generations every year (Miller, 1962).

Etymology

• Catriona. Scottish and irish form of Katherine, which is derived from the greek “katharos”, meaning “pure”. Evelyn Marcus, a respected Brazilian malacologist (born in Germany), often used literary or culturally inspired names in taxonomy. While she did not always explain the names she coined, they frequently had personal, aesthetic or linguistic significance.
• Aurantia, from Latin “aurantiacus”, golden colored.

Distribution
From Norway to Bretagne and around the British Isles, as well as south to the Bay of Biscay. It has also been found in Galicia, Spain (Trigo et al., 2018, as C.gymnota). Schmekel and Portmann (1982) describe it (as C. gymnota) from the western Mediterranean but they probably refer to another species, like Trinchesia sp.2 in Prkić et al. (2018). It appears to be scarce in, or absent from, southern Iberia and the Mediterranean.

More pictures

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

• AsturNatura
• Biodiversity Heritage Library
• BiologiaMarina.org
• DORIS
• Encyclopedia of Marine Life of Britain and Ireland
• European Sea Slugs by Morddyn
• Flickr pictures
• Interim Register of Marine and Nonmarine Genera
• NCBI GenBank
• OBIS - Search by Taxon
• Scottish Nudibranchs
• The Conchological Society of Great Britain and Ireland
• World Register of Marine Species

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