Scyllaea pelagica

Scyllaea pelagica  Linnaeus, 1758

Scyllaea pelagica by Enrico Ricchitelli

Taxonomic note: Traditionally regarded as a single circumtropical species, molecular studies have suggested that Atlantic and Indo-Pacific populations may correspond to distinct species: the name Scyllaea pelagica is applied to Atlantic specimens, while the name Scyllaea fulva has been reinstated for Indo-Pacific material (Pola et al., 2012).

Synonyms

• Scyllaea edwardsii A. E. Verrill, 1878
• Scyllaea grayae A. Adams & Reeve, 1850
• Scyllaea hookeeri Gray M.E., 1850
• Scyllaea marmorata Alder & Hancock, 1864
• Scyllaea pelagica var. marginata Bergh, 1871
• Scyllaea punctata Bouchard-Chantereaux, 1835
• Scyllaea viridis Alder & Hancock, 1864

Description
A robust, dorsoventrally flattened nudibranch that can reach about 10 cm in length. The anterior end of the body bears two pairs of sensory tentacles and a pair of rhinophores protected by broad sheaths. On each side of the body there are two pairs of lateral lobes with dentate margins and truncated tips, known as “cerata”, which contain numerous small gills on their inner surface. The skin is generally smooth, with a few scattered conical tubercles. The typical coloration is yellowish-brown or greenish, often with small white markings; in some individuals a line of bright blue dots runs along the flanks.

Biology
A pelagic species that usually lives among floating masses of brown algae of the genus Sargassum, where it feeds mainly on the hydroids growing on these algae. The egg mass is deposited in gelatinous ribbons attached to the sargassum, from which planktonic larvae emerge. If detached from the alga it can swim to a limited extent by flexing its body. Laboratory experiments using radioactive carbon labelling have shown that, in oligotrophic environments such as the Sargasso Sea, its larvae can directly incorporate dissolved amino acids from the water through the skin and the cerata.

Etymology

• Scyllaea. Derived from Greek “skylla”, a sea nymph transformed into a marine monster that terrified seamen.
• Pelagica. From Greek “pelagikos”, derived from “pelagios”, of high seas.

Distribution
This species shows a mainly pantropical and subtropical distribution, associated with floating masses of brown algae of the genus Sargassum, on which it lives and disperses in the open ocean. Its presence is well documented in the Atlantic, Indian and Pacific oceans, especially in regions where large pelagic aggregations of Sargassum occur (Rudman, 2005; WoRMS, 2024). In the Mediterranean Sea, however, the species is considered rare and with very few records. Historical reports exist from the Aegean Sea, already mentioned in the 19th century (Forbes, 1844), and later confirmed in reviews of the opisthobranch fauna of Greek waters, where it remains a rarely encountered taxon (Zenetos et al., 2016). More recently, additional observations have been published from the eastern Mediterranean, including documented records from Cyprus (Pernera Beach, Ayia Napa) at depths between 5 and 7 m, representing the first confirmed record for that area (Kampouris & Constantinou, 2022). In the western Mediterranean, the species has recently been observed on the Catalan coast during the citizen science campaign “BioMARató”, suggesting that its presence may be related to passive transport events via floating algae or surface currents from the Atlantic (MINKA, 2025). Available data indicate that the species does not form stable populations in the Mediterranean and that its occurrence likely reflects occasional dispersal events linked to its pelagic ecology.

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
• Encyclopedia of Marine Life of Britain and Ireland
• Flickr pictures
• Interim Register of Marine and Nonmarine Genera
• NCBI GenBank
• Nudibranchs of the Sunshine Coast
• OBIS - Search by Taxon
• SeaSlug Forum
• The Slug Site
• The Vibrant Sea
• World Register of Marine Species

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