July 2, 2003
From: John Chuk
This is not a great image but it may be of interest. It is an in situ shot of a rather well camouflaged, dark shaded specimen of Rostanga australis photographed at Flinders Pier, Victoria, Australia on 20 March 2003. The specimen measured 25mm in length and was found on a dark purple sponge, on a pier pylon, at a depth of 3.5m. A portion of a pale egg ribbon is seen protruding from under the anterior border of the specimen.
The dorsum has a somewhat reticulate pattern of very dark brown spots on a brown background. The submarginal mantle glands appear distinctly yellow in colour and there is a vague line of fine yellow spots running in the midline between the rhinophores and gills. Fine pale spots also encircle the gills. I have found several similar specimens in the past year and all were very difficult to spot in natural light.
It would seem that the species is quite variable in shade from pale pink-cream to dark brown. It is a range of shades that rather matches the range of shades seen in the food sponge on which it is usually found.
It is an interesting find. I have never seen one quite this mottled brown colour before. It does indeed sem to be very variable in colour