Pleurobranchus weberi (Bergh, 1905)

Description

A large pleurobranch, about 10 cm long in life. The dorsum is deep purple-red with about 14 large, slightly projecting discs (up to 20 mm in diameter), each surrounded by two very narrow white rings; the rhinophores are the same purple-red. In alcohol the unworn parts are blackish-brown with a faint whitish central papilla on each disc and dim narrow whitish rings around it.

The form is the typical pleurobranch type. The median anterior notch of the dorsum is faint; the discs are evident only on the dorsum proper, each with a slightly projecting central papilla; the rest of the dorsum is smooth with only fine granulation. Almost half of the gill projects free, with two rows of rachidial knobs corresponding to about 30 leaf pairs. The genital folds are strong, the foot is roughly the same length and width as the dorsum, and the caudal gland is well developed.

Geographic variants reported include a form from Ambon Reef with smaller discs (3-9 mm) bearing slightly projecting central papillae, and an Elat-form from the west coast of Great Kei with oval discs lacking distinct central papillae and bordered by two ~1 mm-wide white garlands.

Distribution

Type locality: a reef off Saleyer (Selayar Island), south of Sulawesi, Indonesia (Siboga station 213). Material from multiple localities across the eastern Indonesian archipelago was already reported in the original description, and the species is now known to range widely across the tropical Indo-West Pacific on coral-reef rock and rubble.

Etymology

The specific epithet weberi commemorates Max Wilhelm Carl Weber (1852-1937), the Dutch zoologist who led the Siboga Expedition (1899-1900).

Remarks

Oscanius Leach (the genus in which the species was originally described) is now treated as essentially synonymous with Pleurobranchus Cuvier, and the species is accordingly placed in Pleurobranchus; the parentheses in the author citation reflect this transfer.

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References

• Oscanius Weberi Bgh. n. sp., Bergh R. (1905). Die Opisthobranchiata der Siboga-expedition. https://doi.org/10.5962/bhl.title.11223
• アカテンアミメフシエラガイ（仮称）, 益田一. (1999). 海洋生物ガイドブック. 東海大学出版会.
• ガンモンフシエラガイ（新称）, 中野理枝. (2018). 日本のウミウシ. 文一総合出版.