Pleurobranchus mamillatus Quoy & Gaimard, 1832

Description

A very large pleurobranch reaching up to 500 mm in length. Body colour is highly variable, ranging from pale brown through orange-yellow to reddish brown. The dorsum bears rounded knob-like tubercles, several of which elongate into conical projections; the bases of the tubercles are flushed with pink that the animal can flash on and off. Unlike most congeners, this species is active by day rather than hiding in crevices.

Distribution

Indian Ocean and western Pacific. Records include Tanzania, Korea and Japan. The type locality is the harbour of Port Louis, Mauritius (Île-de-France), where Quoy & Gaimard observed the species on coral reefs in the harbour roads.

Etymology

The specific epithet mamillatus is the Latin for "having nipple-like prominences" (from mamilla, "nipple"), referring to the conspicuous dorsal tubercles. The Japanese vernacular イッサイフシエラガイ comes from the Issai district of Ōtsuki Town in Kōchi Prefecture.

Remarks

Originally described in Voyage de l'Astrolabe, Zoologie (Paris, Tastu, 1832, T.2 pt.1: 294). Quoy & Gaimard noted that the animal "swallows fairly large gravel, among which it finds, like sea cucumbers, the small organisms that nourish it" and that the soft consistency is preserved even in the strongest spirit.

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References

• Pleurobranchus mamillatus, Quoy J.R.C. & Gaimard J.P. (1832-1834). Mollusques. In: Dumont d'Urville J. (ed.) Voyage de la corvette l'Astrolabe exécuté par ordre du Roi pendant les années 1826-1827-1828-1829, Zoologie. Tome 2, parts 1 (1832) & 2 (1833). J. Tastu, Paris.
• 高岡生物研究会. (2002). 日本海のウミウシ. 第2版.
• プレウロブランクス・マミラトゥス, 殿塚孝昌. (2003). ウミウシガイドブック〈3〉. TBSブリタニカ.
• プレウロブランクス・マミラートゥス, 小野篤司. (2004). 沖縄のウミウシ. ラトルズ.
• イッサイフシエラガイ（新称）, 中野理枝 & 松田早代子. (2016). 高知県一切において採集したゼニガタフシエラガイ属ウミウシ Pleurobranchus mamillatus Quoy & Gaimard, 1832 の報告と和名の提唱. ちりぼたん. 46(3-4): 132-136.