Cuthona perca

Cuthona perca (Er. Marcus, 1958)

Cuthona cf. perca @ Etang de Thau, France by Héléna Palandri

Taxonomic note. Cuthona perca was originally described by Er. Marcus (1958) under the name Catriona perca. The species was later transferred to the genus Cuthona, adopting the current combination Cuthona perca (Er. Marcus, 1958). It should be noted, however, that the classification of “tergipedid” nudibranchs has undergone substantial revision in recent years. The molecular study by Cella et al. (2016) demonstrated that the former family Tergipedidae was polyphyletic and proposed a new delimitation of clades within the superfamily Fionoidea. Subsequently, Korshunova et al. (2017) reinstated several traditional families -including Cuthonidae- and revalidated classical genera such as Cuthona and Trinchesia, among others. Accordingly, the current placement of Cuthona perca is within the family Cuthonidae, although the phylogeny of the group remains complex and may vary slightly depending on the authors.

Synonyms

• Catriona perca Ernst Marcus, 1958 (Edmunds 1964)
• Trinchesia perca Marcus & Hughes 1974
• Cuthona reflexa Miller, 1977

Description
Very small nudibranch, with a body measuring between 5 and 15 mm (the Adriatic specimen measured 6 mm). The overall appearance is translucent, with grey or cream tones that allow the greenish-brown internal organs to be seen through the body wall. The head is rounded, with smooth rhinophores and cephalic tentacles shorter than the rhinophores. In front of the rhinophores there is a darkly pigmented area, regarded as a distinctive feature of the species. It bears numerous digitiform cerata, translucent and marked by a characteristic subapical white band; the internal digestive gland, also greenish-brown, is visible by transparency. The cerata are arranged in 6–10 transverse rows in dorsolateral position along the body. Both the dorsum and the cerata show numerous small, opaque white spots. The foot has a rounded anterior margin and tapers into a pointed tail.

Biology
This species is considered typical of anthropized coastal habitats such as estuaries, coastal lagoons, harbours, floating pontoons, and ship hulls. It has been recorded in fouling communities covering submerged hard substrates, often associated with human activity, as it tolerates changes in substrate, salinity, and the environmental conditions characteristic of ports and estuaries. It appears to feed on hydrozoans, from which it incorporates nematocysts into its cerata as a defensive mechanism.

Etymology

• Cuthona. From the Greek “keytho” or “kytho”, meaning to hide or conceal.
• Perca. The origin of the name is not documented in Marcus’s (1958) original work.

Distribution
It has been recorded in the western Atlantic Ocean, from Florida to Brazil, including the Caribbean Sea. In the eastern Atlantic it has been reported from Ghana (Edmunds, 1977). In the Mediterranean it has been recorded from the Venice Lagoon (Perrone, 1995), where it is considered an introduced species. It has also been found in the Pacific Ocean: associated with Haliplanella luciae in San Francisco Bay (USA), with the anemone Aiptasia sp. in Hawaii (Gosliner, 1980), and in New Zealand. Its presence in the Black Sea (Martynov et al., 2007) is also noteworthy, where it is thought to be an introduced species resulting from human activity. In November 2025 a specimen was recorded in the Thau Lagoon (France), an area where non-native species are frequently observed. Mediterranean records and those from other regions outside its original range are considered occasional occurrences, and the species does not appear to establish large-scale stable populations.

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

• Biodiversity Heritage Library
• CIESM Atlas of Exotic Species in the Mediterranean
• Flickr pictures
• Interim Register of Marine and Nonmarine Genera
• NCBI GenBank
• NEMESIS - National Exotic Marine and Estuarine Species Information System
• OBIS - Search by Taxon
• Sea Slugs of Hawaii
• World Register of Marine Species

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