Armina japonica (Eliot, 1913)

Description

Dorsum dark, marked with regularly arranged longitudinal pleats in pale grey or yellow. The body bears several longitudinal lateral plates running parallel along the sides. Maximum length about 50 mm. Lives in well-flushed sandy and muddy-sand bottoms — from intertidal seagrass meadows and tidal flats down to subtidal depths — burrowing into the substrate. Feeds on sea pens (Pennatulacea).
Closely resembles and is often confused with Armina semperi; the two are distinguished by the arrangement of the lateral plates, which run vertically (parallel) in A. japonica and obliquely in A. semperi. The number of dorsal pleats and lateral plates increases with growth and is not a reliable diagnostic character.

Distribution

Coastal waters of Japan from Aomori Prefecture south to Kyushu, on both the Sea of Japan / East China Sea side and the Pacific side. Type locality: Misaki, Sagami Bay (muddy bottom).

Etymology

The specific epithet japonica is the Latin for "Japanese" and refers to the type locality.

---

References

• Pleurophyllidia japonica n. sp., Eliot C.N.E. (1913). Japanese nudibranchs. Journal of the College of Science, Imperial University of Tokyo. 35(1): 1-47, pls. 1-2.
• Armina japonica, Baba K. (1949). Opisthobranchia of Sagami Bay collected by His Majesty the Emperor of Japan (相模湾産後鰓類図譜). Iwanami Shoten, Tokyo. 4+2+194+7 pp., pls. 1-50.
• 高岡生物研究会. (2002). 日本海のウミウシ. 第2版.
• タテジマウミウシ, 西田和記. (2024). ウミウシの生態観察図鑑. 誠文堂新光社.