Chromodoris decora
(Pease, 1860)

Order: NUDIBRANCHIA
Suborder: DORIDINA
Family: Chromodorididae

DISTRIBUTION

Tropical and subtropical Pacific and Indian Oceans.

PHOTO

Upper: Colour form with white Y-shaped pattern on back. Iluka, northern New South Wales, Australia. March 1982. 2 mm long alive, AM C132942. Lower: Colour form with purple spots in centre of back. Noumea, New Caledonia, October 1988. Grows to approximately 20 mm long. AM C 156627. Photos: Bill Rudman.

The background colour of the mantle is a translucent straw colour. There is considerable colour variation but the most distinctive feature is an opaque white line running down the dorsal midline which bifurcates to form an inverted Y.

At the mantle edge there can be a thin opaque white line whic is often broken into a series of white spots or patches. Inside this is a broad translucent orange band which obscures the dendritic opaque white mantle glands. There is a thin opaque white line which runs around the mantle, parallel to the edge, just encircling the rhinophore and gill pockets.  Between this intense white line and the orange border the mantle is dusted with white or bluish white but not so intensely as the thin line.  Outside the thin white line the mantle skirt is scattered with reddish purple or purple spots of varying sizes.

From between the rhinophores a thin white line runs down the dorsal midline to midway where it bifurcates to form a loop around the gill pocket.  The rhinophores are a translucent straw colour with an opaque white core and the simple gills are similarly coloured, the lamellae being a creamy-brown straw colour with the interior of each gill opaque white.

There is some variation in colour pattern and sometimes the purple spots on the orange border are few or absent.  Also, the region between the orange band and the white line encircling the gills and rhinophores varies from being as unpigmented as the central region to almost as heavily pigmented as the white line.  In other specimens the Y-shaped white line and the encircling white line can be scattered with purple spots, and in others the Y-shaped line can be broken or have extra branches.

However, in all specimens studied the basic colour pattern can be found with an orange border, a white ring running around the mantle just outside the gills and rhinophores, a white median line bifurcating midway down the body to form a loop around the gill pocket, and a row of large diffuse purple spots between the orange border and the thin white outer ring.

The mantle is elongately ovate with a wide mantle overlap. The simple gills are arranged in a circle, open posteriorly, around the anus.  Large dendritic mantle glands form a submarginal band all around the edge of the mantle beneath the orange margin.

Colour variations are discussed more fully in a separate message [#20717 ]

• See Chromodoris cf. decora
• See Chromodoris decora Colour Group

• Pease, W.H. (1860). Descriptions of new species of mollusca from the Sandwich Islands. Proceedings of the Zoological Society of London, 28: 18-37.
• Rudman, W.B. (1984) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: a review of the genera. Zoological Journal of the Linnean Society 81: 115-273.
• Rudman, W. B. (1986) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Noumea purpurea and Chromodoris decora colour groups. Zoological Journal of the Linnean Society 86(4): 309-353.

Authorship details
Rudman, W.B., 2007 (September 13) Chromodoris decora (Pease, 1860). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/chrdec

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