Risbecia tryoni from Cook Island, Tweed Heads, NSW

June 12, 2006
From: Ian Banks

Bill,
These 2 Risbecia tryoni were observed on the North Side of Cook Island, Tweed Heads, NSW.

Locality: Cook Island, Tweed Heads , 12 metres, New South Wales, Australia, Pacific Ocean, 26 May 2006, Rocky Reef. Length: 4 cm. Photographer: Ian Banks.

Regards Ian

ianbanks@bigpond.com

Banks, I.W., 2006 (Jun 12) Risbecia tryoni from Cook Island, Tweed Heads, NSW. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16831

Dear Ian,

When I first saw your photos I thought the two animals were mating, but then I noticed that the two were left side to left side, rather than right side to right side. Nudibranchs have their genital openings on the  right side, in the anterior quarter of the body, so for two animals to mate they need their right sides together, and their heads to be much closer to each other than in these photos.

On reflection, I think this is an example of two animals 'trailing' - that strange phenomenon where one animal follows another often with the 'follower' usually having its head on the posterior end of the foot of the 'leader'. Perhaps trailing is a prelude to mating, but if so the animals need to reorient themselves.

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Jun 12). Comment on Risbecia tryoni from Cook Island, Tweed Heads, NSW by Ian Banks. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/16831

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