Searching for Macleay’s Spurilla

I am trying to solve a 152 year old ‘cold case’ in the world of nudibranchs. In 1864, the pioneering Australian marine biologist George Angas published a scientific paper naming as new species 30 nudibranchs (both dorids and aeolids) that he collected from Sydney Harbour between 1858 and 1860. Some of Angas’s species, like the Splendid Nudibranch (Goniobranchus splendidus), are well known and familiar nowadays, but about one-third of them are mysteries because Angas’ descriptions and hand-drawn sketches have proven insufficient to recognise them ever again. One of the lines of my research has been to make sense of Angas’ remaining ‘problem children’ because of the significance they bear for Australian, indeed Indo-Pacific, sea slug knowledge. So I would describe myself as a taxonomic detective.

Arguably the most mysterious of all is the aeolid that Angas named as Aeolis macleayi (see photo). Partly because the description is so inadequate, people have simply guessed at what it might be. It has been transferred to the genus Spurilla [for example, Neville Coleman called it Spurilla macleayi in the original version of Nudibranchs Encyclopedia in 2008] or Baeolidia [for example, Gary Cobb called it Baeolidia macleayi in his tribute edition of the book with the same title in 2015]. In fact, I suspect it does not belong in any of these three genera. Unfortunately most of the images that supposedly show it on the web are definitely incorrect.

So I urgently need a specimen of Macleay’s Spurilla. This will be a detective challenge, as this nudibranch is small and lives among rocks in the shallows. We don’t have any physical specimens on file, nor do we have any accurate photographs. My research will include a genetic component to reveal its true identity (that is to redefine it as a species) and also to reveal its closest relations at the generic level.

The species urgently needs clarifying and the name establishing with certainty. In terms of redefining a species, I will make the individual sample that has been characterised and genotyped the name-bearing specimen (the neotype) for this species. That neotype specimen will have been well-travelled by the time it finally makes it to the research collection of the Australian Museum where I will lodge it for posterity. The preserved specimen will come here to Darwin to me first, then go to Dunedin where the genetic analysis will be conducted, then back to Darwin, and finally permanently to Sydney.

So for those who might like to go searching for A. macleayi, what does it actually look like? I have sourced a photo taken by Ken-ichi Ueda (does anybody know him?) of a specimen that appears to match Angas’ original description quite well.


Photo © Ken-ichi Ueda


Its size is about 20 mm. When it is crawling actively, much of its back is exposed (this exposed dorsum is very obvious in Angas’ drawing) and carnelian yellow. There is a large vivid orange patch over the heart in the centre of the back. The finger-like respiratory processes on the dorsal surface (called cerata) are grayish with a distinctive creamish ring just below the tip. As you probably know, all aeolids store the stinging cells of their prey in special sacs at the tips of their cerata for use in their own defense.

Rediscovering a specimen from Port Jackson [the neotype should ideally come from the original locality] will be no easy task. Obviously Sydney Harbour, as it is called now, has undergone profound changes over the last 150 years. And to make things worse nudibranchs are inherently fickle in time and space. ‘Willan’s Law’ states that you’ll never find your target nudibranch on the first attempt. I have spoken with John Turnbull about this challenge, and how to find and collect possible samples. I believe he will be organising a couple of search expeditions with URG at Camp Cove on the low tide. Thanks in advance for helping me with this mystery!