Range extension for Volvatella ayakii

September 21, 2005
From: Julie Marshall

Dear Bill,

I sent you these photos of Volvatella ayakii in early May but I think they must have got lost in the system! I think this species has previously only been reported from Japan. Bob Burn found 14 specimens from sieving Caulerpa racemosa from the reef flat at Heron Island at low tide in March. They ranged in size from 4.5 to 11 mm. The first of the pictured animals was 6.5 mm (shell length 5 mm) and the other photo was 11 mm (shell length 8.5 mm). When Hamatani (1972) described this species he noted that "the body is furnished with numerous white opaque dots over the whole part under the shell and especially densely along the anterior border of the head shield, on rhinophoral-like protruberances, on the dorsal side of foot-corners, at the posterior end of the foot..." The first photo especially clearly shows these opaque white dots.

Locality: Heron Island, Great Barrier Reef, Queensland, Australia. Intertidal. Upper: Length: 6.5 mm  8 March 2005. Lower: Length: 11 mm, 16 March 2005. Photographer: Julie Marshall

  • Hamatani, I. (1972). A new species of Volvatella Pease, 1860, found in the "Caulerpan Microfauna" in the province of Kii, Middle Japan. (Opisthobranchia: Sacoglossa). Publications of the Seto Marine Biological Laboratory, 21: 13-20, Figs 1-3, Pls 2, 3.


Marshall, J.G., 2005 (Sep 21) Range extension for Volvatella ayakii. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/14787

Dear Julie,
Sorry I didn't post your message earlier. The system didn't lose it - I just put it to one side as I wanted to check on the identity of your animals and of course I got side-tracked. What I was wondering about was the relationship between your animals and Volvatella angeliniana, which also has white spots. It is possible the small white spots in your animal are the same as the white spots in Hamatani's description, but looking at his black & white photos the white spots seem to be arranged in a couple of wide bands, one of which is associated with the gills. I am also intrigued by the faint yellowish band along the anterior mantle edge and on the posterior 'spout', and what appear to be a yellowish tip to the rhinophores.  At this stage I would think that V. angeliniana is a distinct species, but perhaps it represents a juvenile stage of V. ayakii.

I am afraid I am not too sure of the identity of this species. The shell shape is very plastic, especially in preserved specimens, but it is one of the main distinguishing features mentioned by Hamatani. Animals already identified as this species from Japan, on the basis off shell shape, don't show the white spots. The white spots in Hamatani's photos seem to be the small secretory glands found in the mantle and skin of most species of this group so it is possible if they have been recently emptied, that they appear to be absent. I will keep your animals as V. ayakii, but it is possible the upper one is V. angeliniana and the lower one is V. ayakii, or even V. vigourouxi but I find identifying many of the species in this genus very problematical.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Sep 21). Comment on Range extension for Volvatella ayakii by Julie Marshall. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/14787


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