Author: (Rudman, 1986)

Order: Nudibranchia  Family: Chromodorididae

Maximum Size: 90 mm

Sightings: Sunshine Coast

Ardeadoris rubroannulata (Rudman, 1986)

A large nudibranch (up to 90 mm) of the Chromodorididae family, Ardeadoris rubroannulata is another species that seems to have a limited Coral Sea distribution only, being reported from New Caledonia, Lord Howe Island and the east coast of sub-tropical Australia although reports are received occasionally from further south. It has been most commonly sighted in southern Queensland, Australia. A couple of sightings have been reported from Indonesia but it is interesting to note that those specimens, among other differences, seem to either lack the distinctive submarginal red line upon the mantle and foot or at best it is very diffuse It may transpire in time that these are separate species.

Ardeadoris rubroannulata has a smooth central mantle of an apricot to golden yellow colour with a mantle margin of three colour bands. The outermost is of a golden yellow with concentric submarginal bands of red then white on both the dorsal and ventral surfaces. Sometimes the red line may be located within the white as it is in the specimen depicted in the main image above. The colour pattern of the mantle margin is repeated upon the edge of the foot with the remainder of the sides of the foot being white. The mantle is wide and overlaps the body. Its edge is extremely convoluted and thickened or puffy. The lamellate rhinophores have a red stalk and brown clavus with a white streak up both the anterior and posterior axes. The rhinophoral pocket is edged in white. The gills are simple but long and large in number, 19 to 22 being the most often quoted numbers and are spirally arranged around the anus. The gills are translucent white with red axes and white tips. The gill pocket is also rimmed in white.

When the animal is crawling and the gills are fully extended they can be seen to be constantly twitching. The mantle glands, mostly concentrated in the white submarginal band, discharge a large amount of white noxious fluid when the animal is sufficiently irritated, as a defence against predators. The dense convolutions of the mantle edge serve to increase the concentration of defensive glands encountered by a predator’s bite.

The spawn is laid as a spiral ribbon, on edge, and has an outwardly sloping coil because the free edge is longer than the fixed edge. It is cream coloured with bright yellow spots of extra-capsular yolk.

Ardeadoris cruenta is somewhat similar in external appearance except that it exhibits red spots rather than the continuous submarginal red line and the rhinophore stalks are the same colour as the central mantle as are the gills.

Altogether this is a large, beautiful and vibrantly coloured nudibranch unpredictably encountered but not uncommon in the indicated regions.

Previously known as Glossodoris rubroannulata and prior to its formal description as Casella sp.

Originally described as Glossodoris rubroannulata

Above: Ardeadoris rubroannulata feeding.

David A. Mullins, December 2019

References:
– Willan, R.C. & Coleman, N. (1984). Nudibranchs of Australia, Neville Coleman, AMPI: 28-29

– Rudman, W.B. (1986) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: The genus Glossodoris Ehrenberg (= Casella, H. & A. Adams). Zoological Journal of the Linnean Society 86(2): 101-184.

– Marshall, J.G., Willan, R.C. (1999). Nudibranchs of Heron Island, Great Barrier Reef: A survey of the Opisthobranchia (sea slugs) of Heron and Wistari Reefs; Backhuys: Leiden, The Netherlands, 1999.

– Wilson, N.G. (2002) Egg Masses of Chromodorid Nudibranchs (Mollusca: Gastropoda: Opisthobranchia). Malacologia, 2002, 44(2): 289-305.

– Rudman, W.B., Bergquist (2007) A review of feeding specificity in the sponge-feeding Chromodorididae (Nudibranchia: Mollusca). Molluscan Research, 27(2): 60-88.

– Rudman, W.B., 2007 (Aug 31). Comment on Glossodoris rubroannulata – natural history [1] by David Mullins. [Message in] Sea Slug Forum. Australian Museum, Sydney.

– Rudman, W.B., 2007 (Aug 31). Comment on Glossodoris rubroannulata – natural history [2] by David Mullins. [Message in] Sea Slug Forum. Australian Museum, Sydney.

– Johnson, R.F., Gosliner, T.M. (2012). Traditional taxonomic groupings mask evolutionary history: A molecular phylogeny and new classification of the chromodorid nudibranchs. PLoS One 7 (4): e33479.

– Nimbs, M.J., Smith, S.D.A. (2017). An illustrated inventory of the sea slugs of New South Wales, Australia (Gastropoda: Heterobranchia). Proceedings of the Royal Society of Victoria 128: 44-113.

– This Species Profile has been modified from:
– Opisthobranch of the Week, Week #754, Glossodoris rubroannulata (29/08/2011), Mike Miller’s  slugsite.tierranet.com by David A. Mullins
– A previously published article in Dive Log Magazine’s – Critter ID with NudiNotes Column, Issue: #347 (June 2017): 12 by David A. Mullins