Re: Halgerda gunnessi from Rottnest Is, W. Australia

Thanks Adrian,
This is a welcome addition, as it clearly shows the edge of the mantle and the foot. I had thought from the original description and photo of this species that Halgerda gunnessi had a yellow border, but the actual wording 'The mantle margin has the same yellow coloration outlined in white' refers to the colour of the ridges so it means there is a white edge and a yellow submarginal line.

In colour therefore there is no real difference between this species and Halgerda theobroma that couldn't be considered part of a variation from many ridges to few. Both species have very similar radular morphology and both are only known from Rottnest Island. Unfortunately Fahey & Gosliner (2001) did not really discuss the possibility that the colour similarity of these two species may be intraspecific because they considered the one anatomical difference between the two - the presence of a vaginal gland in H. theobroma - to conclusively preclude a close relationship. Perhaps that is a reasonable approach, but considering the similarity between these two species I would think it would be worth investigating whether this vaginal gland develops at a certain stage in the life cycle or perhaps has a cyclical appearance?

It is certainly an interesting question. Perhaps it would be a worthwhile 'project' when visiting Rottnest in the future to keep a look out for specimens of Halgerda theobroma and H. gunnessi to see if you can find some intermediate colour forms
Best wishes
Bill Rudman