Placida dendritica in northern NZ

January 10, 2007
From: Ian Skipworth

Hi Bill

I was interested to see the recent message [#19156]  on Placida dendritica in northern New Zealand.

Coincidentally, I was diving at the Poor Knights Islands (northeastern
NZ) last weekend and observed a number of small slugs which I was unfamiliar with but which appear similar to the Placida dendritica photos on the Forum.

Locality: Poor Knights Islands, 10m, New Zealand, Pacific Ocean, 07 January 2007, Rocky reef. Length: 4mm. Photographer: Ian Skipworth

I saw a fair number of these on two dives. They are probably 3 to 4 mm long and somewhat camouflaged amongst alga so are not easy to see with the naked eye and rather difficult to get a good photo of. From what I saw in the weekend, I suspect they are currently very common at the Poor Knights and think you'd have little difficulty finding them if you know what you're looking for.

Cheers
Ian

ianskip@xtra.co.nz

Skipworth, I.R., 2007 (Jan 10) Placida dendritica in northern NZ. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/19187

Dear Ian,
Thanks for the rapid response. Looking at your photos makes me wonder whether it is the same as the south-eastern Australian species, but hopefully Cynthia Trowbridge and others working on this complex of species will put us out of our misery soon. Sherman Bleakney (1989) decided Placida dendritica was a worldwide species but more recent work suggests there are a number of distinct regional species. If this proves true then the New Zealand animal, and perhaps its southeastern Australian look-alike, will revert to the old name Placida aoteana (Powell, 1937).

Smaller animals in Sydney look much like your photos, but as they grow they tend to become broader in the body with more flattened cerata.

• Bleakney, J.S. (1989) Morphological variation in the radula of Placida dendritica (Alder & Hancock, 1843) (Opisthobranchia: Ascoglossa/Sacoglossa) from Atlantic and Pacific populations. The Veliger, 32: 171-181.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Jan 10). Comment on Placida dendritica in northern NZ by Ian Skipworth. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/19187

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