Cyerce elegans Bergh, 1870

Description

A small sacoglossan, about 3.5 cm long in life with the body up to about 3 cm across including the laterally projecting cerata. The body is almost water-clear, faintly yellowish-white, especially translucent in the cerata and less so in the body. The dorsum is framed by an anteriorly open, elongate horseshoe-shaped arch from which branches run to the innermost cerata; at the base of each ceras one or several green dots produced by peculiar internal yellow bodies appear in life, and the margin of each ceras is speckled with larger reddish-brown spots (usually 5-9 per ceras, sometimes fewer). The cerata are arranged in roughly four longitudinal rows on each side, with the innermost row largest (about 8-9 cerata per side) and the outermost smallest; the largest cerata reach 7-9 mm long. Each ceras is inflated, leaf-like and petiolate, with a thick blade rounded at the margin and crossed by fine white lines often converging along a midline. The body is unusually gelatinous and translucent — through the dorsum the eyes, the central nervous system and parts of the gut can be seen. Eyes show through clearly at the base of the rhinophores. The rhinophores reach up to 4.5 mm in the largest individuals, and the oral tentacles about half that.

Distribution

Type locality: Aibukit, Palaos (Pelew) Islands, western Pacific. The species is now known to range widely across the tropical Indo-West Pacific.

Etymology

The Latin adjective elegans means "elegant, refined" — a descriptive epithet evoking the semi-transparent body and the patterned margins of the leaf-like cerata.

Remarks

The species is the type of the genus Cyerce. The Japanese name sukesuke-furiru-umiushi ("see-through frill sea slug") refers to the translucent body and the frilly margins of the leaf-like cerata.

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References

• Cyerce elegans (Semper) Bgh. n. sp., Bergh L.S.R. (1871). Malacologische Untersuchungen. In: C. Semper (ed.), Reisen im Archipel der Philippinen, Wissenschaftliche Resultate. Theil 2, Band 2, Heft 2: 49-118, pls 9-16.
• スケスケフリルウミウシ, 益田一. (1999). 海洋生物ガイドブック. 第2刷. 東海大学出版会.
• Cyerce sp. 3, Terrence Gosliner, Ángel Valdés and David Behrens. (2018). Nudibranch and Sea Slug Identification Indo-Pacific 2nd Edition. New World Pubns Inc.
• Cyerce elegans, Moreno K., Medrano S., Gosliner T.M., Wilson N.G., Krug P.J. & Valdés Á. (2025). Phylogenetic systematics of the genus Cyerce (Mollusca: Heterobranchia: Sacoglossa: Caliphyllidae) from the Pacific and Indian oceans with descriptions of nine new species. Zoological Journal of the Linnean Society. 204(1): zlaf030. https://doi.org/10.1093/zoolinnean/zlaf030