Hypselodoris zebrina
(Alder & Hancock, 1864)

Order: NUDIBRANCHIA
Suborder: DORIDINA
Superfamily: EUDORIDOIDEA
Family: Chromodorididae

PHOTO

Taplamu, Thailand. Depth between 12m to 20m. Photo: Danny Van Belle
Lower: Chromodoris zebrina, Madras region, southeastern India. Original painting - Alder & Hancock, 1864: Plate 29, fig 7.

I am sure this is Hypselodoris zebrina, a species which was described about 150 years ago from southeastern India and has never been reported since. I have scanned a copy of the original illustration alongside for comparison (Alder & Hancock, 1864: Plate 29, fig 7).

Here is an extract from the original description describing the colour pattern:
"white with waved crimson stripe down the centre of the back and transverse stripes of the same colour (of unequal lengths) at the sides and around the ends; there are largish yellow spots down each side of the central stripe and between the transverse ones near the margin; a crimson stripe also runs from the cloak along a ridge to the tail. Dorsal tentacles .. with laminated part crimson ... [Gills] simply pinnate, crimson ... Length 2/10 inch" [p123-4].

In the original description, the colour of the stripes and the gills and rhinophores are described as 'crimson' but the illustration would suggest 'purple' may have been a better word to use. Priscilla Yeo's photo, and subsequent photos from Danny Van Belle show the colour variation in this species, in particular the variable nature of the purple median line on the mantle, ranging from a continuous line, to a few spots, and sometimes absent. The yellow spots, radial purple lines, and purple dorso-median line down the posterior foot are all very characteristic features found in no other species of chromodorid.

It has similarities to Hypselodoris kanga, Hypselodoris nigrostriata and Hypselodoris zephyra all with yellow spots, and bluish purple lines, but in those species the gills are triangular in cross-section, while in your animal they are simple. The species was originally placed in the genus Chromodoris. Although no anatomical information is available the general body shape and colour pattern would suggest that it is most likely to be a species of Hypselodoris.

Reference:
• Alder, J. & Hancock, A. (1864) Notice of a collection of nudibranchiate mollusca made in India by Walter Elliot Esq., with descriptions of several new genera and species. Transactions of the Zoological Society of London, 5: 113-147.

Authorship details
Rudman, W.B., 2002 (December 10) Hypselodoris zebrina (Alder & Hancock, 1864). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/hypszebri

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