Re: Need info on New Zealand sea slugs

June 2, 2001
From: Cynthia Trowbridge

Dear Bill and Katherine,

There is a 106 page paperback book available from the Leigh Marine Laboratory:
• Willan, R. & Morton, J. (1984) Marine Molluscs. Part 2. Opisthobranchia. Leigh Marine Laboratory, University of Auckland, New Zealand.

When I worked in New Zealand, I found this book to be very useful to learn the slug fauna and to access the primary literature. Also, another book that may be helpful is the recent book by Graham J. Edgar, Univ. Tasmania. 1997. Australian Marine Life, The Plants and Animals of Temperate Waters. Reed Books, Victoria.

Perhaps, Bill, you could share with the rest of us, to what is the degree of overlap in opisthobranch species between New Zealand and SE Australia? Are most New Zealand opisthobranchs also in Australia? I assume that those with planktotrophic larvae probably are. I would be keen to hear your thoughts on this.

Trowbridge, C., 2001 (Jun 2) Re: Need info on New Zealand sea slugs. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Cynthia,
To answer your question about the relationship between the NZ and SE Australian faunas. I used a recent checklist of NZ molluscs (Spence & Willan, 1996) where there are 138 opisthobranch species (excluding the pteropods) reported from New Zealand. After removing a couple of subantarctic animals and a couple of taxonomic anomalies I divided the remaining 134 species into 3 categories. Those endemic to New Zealand (NZ) those found in both NZ and southern Australia (Aust), and those found in NZ but having a broad distribution in the Indo-West Pacific (IWP).

You will see from the table alongside that there is a characteristic endemic NZ opisthobranch fauna, especially amongst the bubble shells and nudibranchs. There are species common to NZ and southeastern Australia, a phenomenon also evident in other marine molluscs, and a much larger element of species with a wide distribution in the Indo-West Pacific.

New Zealand has a rich endemic fauna of marine molluscs which to a large extent have evolved independently from the Australian fauna since the breakup of Gondwana. At present the prevailing currents in the Tasman Sea are from west to east which explains the occurrence of southeastern Australian elements in the NZ marine fauna. The widespread IWP elements in the fauna have probably been introduced both from Australia and from the large cyclic oceanic water movements which occur in the South Pacific from time to time (El Nino etc).

Thanks for mentioning Willan & Morton's handbook. It is certainly a good introduction, giving biological information on the species covered, but it is by no means comprehensive, dealing only with species that have been recorded from the vicinity of the marine station at Leigh. The other excellent book you mention, by Graham Edgar, includes a broad coverage of the temperate Australian marine fauna and flora, but as I explain above, the NZ fauna and flora is quite distinct.

• Spence, H.G. & Willan, R.C. (1996) The Marine Fauna of New Zealand: Index to the Fauna 3. Mollusca. New Zealand Oceanographic Institute Memoir, 105 (for 1995): [Opisthobranchs on pp 32-37]

Best wishes,
Bill Rudman

Rudman, W.B., 2001 (Jun 2). Comment on Re: Need info on New Zealand sea slugs by Cynthia Trowbridge. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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