Marioniopsis arborescens (Bergh, 1890)

Description

A medium-sized marioniopsid. In alcohol, body length 4-6 cm with maximum width about 1.9 cm. The colour is pale yellowish-green or greenish-yellow; the gill leaves more strongly green; the head and the sole of the foot dirty yellowish-white. The frontal margin bears simple finger-shaped marginal papillae of unequal size. Outside them stand the finger-shaped oral tentacles with a deep groove on the underside. Postero-laterally on the neck are the rhinophore sheaths, with the deeply retracted club of the usual tassel-shape bearing five bipinnate leaves. The dorsum is rather broad and fairly flat, covered all over with small to medium-sized rounded or short-conical knobs. The dorsal margin projects as a thin border, and from it issue the gills at progressively shorter intervals to the rear. The number of gills is usually 4 on each side, rarely up to 10; they branch tree-like, the terminal branches bipinnate.

Distribution

Type locality: Amboina (Ambon, Indonesia). Distributed across the Indo-West Pacific in coral-reef sand and rubble habitats.

Etymology

The Latin arborescens is the present participle of arborescere ("to become tree-like"), in reference to the tree-like branching of the gills.

Remarks

Originally described as Marionia arborescens and later transferred to Marioniopsis; the parentheses in the author citation reflect this transfer. Like other tritoniids, this species is a carnivorous predator of cnidarians (octocorals).

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References

• Marionia arborescens, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• シンリンウミウシ（新称）, 中野理枝. (2018). 日本のウミウシ. 文一総合出版.
• Marioniopsis arborescens, Gosliner, T. et al. (2023). Southern African Sea Slugs. Southern Underwater Research Group Press, 7 Blackwood Drive, Hout Bay 7806, Cape Town, South Africa.