Aplysia gigantea / A. extraordinaria

October 27, 2005
From: Stephen Davison

On Saturday I was diving off Kurnell National Park, Sydney, and saw my first Sea hare! I was flabbagasted at the size of it ( I didn't even know they existed, this my 305th dive!) as i read on your site, trying to id it I noticed the discrepancy with id on Aplysia gigantea / Aplysia extraordinaria. The A. gigantea from Western Australia is EXACTLY like the one I saw off Sydney...

Locality: "Monument park" Kurnell National park, Sydney, NSW, Australia. Depth: approx 10 m. Length: Approx 500-600 mm. 22 October 2005. Rock reef, within 30 m of shore, some kelp. Photographer: Stephen Davison

The colouring was dark reddish brown ( like picture) and the size was more like 600 mm rather than the 400 mm described for the A. extraordinaria. I have some very bad pics wich I may attach but the they are the worst pics I've taken in about 100 dives, I was so amazed at this "over grown snail" I sort of forgot to do much then my buddy was bored and gone! I have better( not much better) MPG video that I might get a decent still off later...
I don't know how heated the debate is about the similarity of the two species but I hope this might help towards some understanding!

In one photo I lamely put my hand in to get scale... doesn't work very well. If I'd realised how significant it might be...!

Stephen Davison


Davison, S., 2005 (Oct 27) Aplysia gigantea / A. extraordinaria. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/15107

Dear Stephen,
Congratulations on your first Aplysia sighting! Fortunately, we are not planning to go to war over the Aplysia gigantea - Aplysia extraordinaria debate, so don't feel guilty about your photos or lack of precise measurement. In fact I don't even know if you could call it a debate. Apart from Fred Wells' paper on A. extraordinaria, in 1986, and my comments on the Forum, I don't think anyone else has joined in.

I am pretty sure they are the same species, and it is possible a large species on the east coast of Africa is the same. There are similar species' doubts which need to be resolved in other parts of the world, such as is the common west Atlantic species Aplysia brasiliana the same as the east Atlantic species A. fasciata?[see #12545]

Unfortunately there are too few marine biologists being supported worldwide for such questions to be high on anyone's priority list. Thanks for letting us know of your sighting. We are building up a lot of valuable information from contributions such as yours.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Oct 27). Comment on Aplysia gigantea / A. extraordinaria by Stephen Davison. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/15107

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