Hypselodoris decorata (Risbec, 1928)

Description

A moderately large chromodorid reaching about 25 mm. The body is long, slender and translucent pink, with four thin continuous opaque white longitudinal lines on the notum. A broad orange band runs along the mantle margins, often with interior undulations and opaque white spots. The anterior and posterior ends bear purple to orange areas dotted with opaque white spots. Rows of reddish to purple spots lie between the white lines, with more diffuse purple pigment toward the periphery. There are seven to eight unipinnate gills with a translucent white base and inner margin and bright red-orange apical surfaces. The perfoliate rhinophores have an opaque white club with two red transverse bands, plus a third red ring on the translucent white base. It reaches about 25 mm in length.

Distribution

Type locality New Caledonia. Recorded from the Marshall Islands, Vanuatu, New Caledonia, Indonesia, Papua New Guinea, the Philippines and Malaysia.

Etymology

The specific epithet decorata is from Latin decoratus, meaning "decorated" or "adorned."

Remarks

Long confused with the similar Hypselodoris maculosa, with which it was once treated as a single species. The two have been separated by the number of red rhinophore rings, three in this species (two on the club plus one at the base) versus two in H. maculosa, but some individuals of H. maculosa also show three rings, so they cannot be reliably told apart by appearance alone. Confident separation requires molecular data.

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References

• Chromodoris decorata, Risbec J. (1928). Contribution à l'étude des nudibranches néo-calédoniens. Faune des Colonies françaises, Tome II: 1-328, 12 pls. (Société d'Éditions géographiques, maritimes et coloniales, Paris). [doctoral thesis monograph]
• Hypselodoris maculosa, Terrence Gosliner, Ángel Valdés and David Behrens. (2015). Nudibranch and Sea Slug Identification Indo-Pacific. New World Pubns Inc.
• Hypselodoris decorata, Terrence Gosliner, Ángel Valdés and David Behrens. (2018). Nudibranch and Sea Slug Identification Indo-Pacific 2nd Edition. New World Pubns Inc.
• Hypselodoris decorata (Risbec, 1928), Epstein H.E., Hallas J.M., Johnson R.F., Lopez A. & Gosliner T.M. (2019). Reading between the lines: revealing cryptic species diversity and colour patterns in Hypselodoris nudibranchs (Mollusca: Heterobranchia: Chromodorididae). Zoological Journal of the Linnean Society. 186(1): 116-189. https://doi.org/10.1093/zoolinnean/zly048