Crosslandia viridis Eliot, 1902

Description

Body colour is highly variable, ranging from bright green through yellow-brown to dark brown, matching the algae or seagrass on which the animal lives. The dorsum is often dotted with small white tubercles and blue or brown markings, although individuals lacking these features are common. A single pair of large, leaf-like cerata is borne dorsally; their tips are sometimes bifid. The rhinophores are housed in sheaths whose margins, together with those of the rhinophores themselves, bear leaf-like lobes. Although superficially resembling sacoglossans of the genus Elysia, Crosslandia viridis is readily distinguished by these lobed rhinophoral sheaths. Reaches about 30 mm in length.

Distribution

Type locality: Zanzibar (Tanzania). Widely distributed in the tropical and subtropical Indo-West Pacific; in Japan recorded from central Honshu southwards.

Etymology

From the Latin viridis ("green"), referring to the bright green coloration typical of the species.

Remarks

Feeds on hydroids epiphytic on seagrasses (notably Thalassodendron) and macroalgae, where its cryptic coloration provides effective camouflage. The Japanese name "コチョウウミウシ" (small butterfly sea slug) was originally proposed based on specimens from Seto, Kii Peninsula, evidently alluding to the wing-like appearance of the leaf-shaped cerata. Crosslandia fusca Eliot, 1902 and C. orientalis Thiele, 1925 are regarded as junior synonyms.

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References

• Crosslandia viridis, Baba K. (1937). Opisthobranchia Of Japan (II). Journal of the Faculty of Agriculture, Kyushu University. 5(7): 289-344. https://doi.org/10.5109/22586
• コチヨウウミウシ（新稱）, 馬場菊太郎 & 濱谷巌. (1952). 紀州産後鰓類目録. 南紀生物. Supplement 1: 1-11.
• コチョウウミウシ, 鈴木敬宇. (2000). ウミウシガイドブック〈2〉. TBSブリタニカ.
• 高岡生物研究会. (2002). 日本海のウミウシ. 第2版.
• Crosslandia viridis, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• コチョウウミウシ, 中野理枝. (2018). 日本のウミウシ. 文一総合出版.