Armina rubida (A. A. Gould, 1852)

Description

A small to medium-sized arminid reaching about 3 cm in body length. The body is lanceolate, posteriorly acuminate, with a narrow reflexed mantle. The dorsum is reddish to lake-red and bears numerous fine longitudinal folds running along the entire length of the body. The head is cowled, forming a small mask projecting in front of the rhinophores, with the eyes set at the outer base of the rhinophores. The foot is bright reddish-purple, while the dorsal surface is slightly paler. Movement is extremely sluggish.

Distribution

Type locality: a coral reef off Honolulu, Oahu, Hawaiian Islands. The species is broadly distributed across the Indo-Pacific, with subsequent records from the Philippines, New Zealand, Japan, and South Africa, in addition to Hawaii.

Etymology

The specific epithet rubida is the feminine form of the Latin adjective rubidus, meaning "ruddy" or "deep red", in reference to the species' red to lake-red body coloration.

Remarks

Dermatobranchus pulcherrimus, originally described from New Zealand specimens, is now treated as a junior synonym of this species. Members of the genus Armina are generally known to feed on sea pens. The Japanese name "アカイオトメウミウシ" ("red Otome-umiushi") dates from when the species was still treated as Dermatobranchus rubidus, and draws on the Japanese vernacular for Dermatobranchus ("Otome-umiushi") together with the reddish body colour.

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References

• Diphyllidia rubida n. sp., Gould A.A. (1852). Mollusca and Shells. United States Exploring Expedition during the years 1838, 1839, 1840, 1841, 1842, under the command of Charles Wilkes, U.S.N. Vol. 12. Boston: Gould & Lincoln. xv + 510 pp.
• Dermatobranchus pulcherrimus sp. n., Miller M.C. & Willan R.C. (1986). A review of the New Zealand arminacean nudibranchs (Opisthobranchia: Arminacea). New Zealand Journal of Zoology, 13(3): 377-408. https://doi.org/10.1080/03014223.1986.10422671
• タテジマウミウシ, 鈴木敬宇. (2000). ウミウシガイドブック〈2〉. TBSブリタニカ.
• デルマトブランクス・ルビウス, 小野篤司 & 加藤昌一. (2009). ウミウシ. 誠文堂新光社.
• Dermatobranchus rubidus, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• アカイオトメウミウシ（新称）, 中野理枝. (2018). 日本のウミウシ. 文一総合出版.
• アカイオトメウミウシ, 小野篤司 & 加藤昌一. (2020). 新版 ウミウシ. 誠文堂新光社.
• Armina rubida, Gosliner, T. et al. (2023). Southern African Sea Slugs. Southern Underwater Research Group Press, 7 Blackwood Drive, Hout Bay 7806, Cape Town, South Africa.