Favorinus japonicus Baba, 1949
- Location
- Taketomi South, Ishigaki and Yaeyama, Okinawa, Japan
- Date
- 2016/05/12
- Length
- 14mm
- Depth
- 12.0m
- Water temperature
- 27.4℃
Description
A small Aeolidacea, body length 8-15 mm. Oral tentacles and rhinophores are present; the rhinophores bear two distinctive spherical swellings at mid-length — a key diagnostic feature. The cerata are long fusiform with many small tubercles on the surface, arranged in 7-8 groups per side: 1st-3rd groups 10 cerata each, 4th-5th 6 each, 6th onward 1-2 each. The first 3-4 groups are mounted on horseshoe ridges; the rest in oblique rows. Ground colour pale yellow, with albuminous diamond-shaped markings arranged front-to-back along the dorsal midline. The cerata are a beautiful red. The masticatory edge of the jaw plate is covered by several rows of spinous teeth, with the outermost row longest. Radula formula 17-20×0.1.0. The central tooth is V-shaped with a long projecting median cusp.Distribution
Type locality is Hayama-Koiso, Sagami Bay (intertidal, August 1940, 2 specimens) and Hayama-Najima-Hiraiwa, Sagami Bay (August 1939, 1 specimen). The original description (Baba, 1949) records the species only from Hayama in Sagami Bay (3 specimens).Etymology
The specific epithet japonicus refers to Japan as the country of origin. The original description does not give an explicit etymology paragraph; the toponymic derivation is self-evident. The Japanese name "Chigo-mino-umiushi" (infant aeolid) reflects the small, charming appearance.Remarks
Distinguished from sympatric Favorinus perfoliatus by the rhinophores bearing two distinct spherical swellings at mid-length (versus many lamellae in Favorinus perfoliatus) and by the pale yellow ground colour (versus pale pink in Favorinus perfoliatus).References
- Favorinus japonicus Baba, 1949, 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.
- チゴミノウミウシ, 小野篤司. (1999). ウミウシガイドブック. TBSブリタニカ.
- チゴミノウミウシ, 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.
- チゴミノウミウシ, 小野篤司. (2004). 沖縄のウミウシ. ラトルズ.
- チゴミノウミウシ, 中野理枝. (2004). 本州のウミウシ. ラトルズ.
- チゴミノウミウシ, 小野篤司 & 加藤昌一. (2009). ウミウシ. 誠文堂新光社.
A Kindle field guide by the site author
Kimoto N. (2026). Sea Slugs of Japan & the Indo-Pacific, 2nd Edition.
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Photos of Favorinus japonicus
Tag:
Same Genus Nudibranchs
Similar Colors Nudibranchs
Academic Database
Sea slug observation data is available in international marine biodiversity databases.