Reticulidia halgerda Brunckhorst & Burn, 1990

Description

A medium- to large-sized phyllidiid; observation records reach about 80 mm in body length. Ground colour is a vivid yellow with the dorsum overlaid in black, across which thin ridges run longitudinally and transversely. The number and arrangement of the ridges vary considerably among individuals.

The ridges themselves are fine white lines, paralleled by yellow stripes that together form a reticulate pattern — the source of the specific name halgerda, evoking the reticulum seen in Halgerda. The rhinophores are smooth and orange-red.

The species is externally near-identical to members of Halgerda but is clearly distinguished by the absence of a circumanal gill plume (characteristic of Phyllidiidae); instead, branchial leaves lie under the lateral mantle folds.

Distribution

Western, central and southern Pacific. Records come from Australia, the Solomon Islands, New Caledonia, Fiji, Papua New Guinea, Indonesia, Taiwan, the Philippines, southern Japan, Tonga and the Marshall Islands. The species occurs on sponges encrusting coral-reef rocks.

Etymology

The specific epithet halgerda alludes to the reticulate dorsal pattern, reminiscent of (but unrelated to) the genus Halgerda Bergh, 1880.

Remarks

Originally described by Brunckhorst & Burn (in Brunckhorst, 1990) from material collected on the eastern coast of Australia. The genus Reticulidia Brunckhorst, 1990 is a small Indo-Pacific phyllidiid genus, all members being sponge-feeders.

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References

• Reticulidia halgerda Brunckhorst & Burn, gen. et sp. nov., Brunckhorst D.J. (1990). Description of a new genus and species belonging to the family Phyllidiidae (Nudibranchia: Doridoidea). Journal of Molluscan Studies. 56(4): 567-576.
• クロカブトウミウシ, 益田一. (1999). 海洋生物ガイドブック. 第2刷. 東海大学出版会.
• レティクリディア・ハルゲルダ, 殿塚孝昌. (2003). ウミウシガイドブック〈3〉. TBSブリタニカ.
• Reticulidia halgerda, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• クロカブトウミウシ, 中野理枝. (2018). 日本のウミウシ. 文一総合出版.