Nembrotha chamberlaini: The ART of laying eggs

September 15, 2009
From: Marcel Tanke

Dear Bill,
Following my message [#22310] of a green form of Nembrotha chamberlaini (which you also refer to as Nembrotha sp. 9), here is a photo of the brown form.

As I like this particular picture, I had it as my PC desktop for a while. So I had quite some time to study it. I here want to share this "study" with you:

The nudibranch has selected a relatively smooth, almost horizontal substrate to lay its eggs. It is producing a beautiful inside out, counter clockwise, yellow egg spiral. When zooming in to it, the individual small eggs in the gelatinous mass can clearly be seen. In the center of the egg spiral, the curvature is highest. As N. chamberlaini in the center of the spiral cannot feel a previously laid, reference egg spiral, it is difficult for the animal to keep a constant distance between the subsequent layers. It can be seen that after, say one and a half round, that becomes easier. Then, as seen in the picture, N. chamberlaini feels and checks the position of the previous round of egg spiral with its left, blue / purple oral tentacle. The upper half of its body is parallel and even touching the previous round of egg mass. And it is actually changing the angle of vertical position of the egg mass on the substrate, by pushing it inside.

The eggs are coming from the female opening on the right side of the body, which cannot be seen in this picture. The eggs are guided into position and pushed against the substrate between the two muscles that are located on both sides of the foot. Visible in the picture is the muscle on the left side of the foot, having the same blue / purple color as the oral tentacle. At the point of leaving the foot of the animal, the vertical position of the egg mass is still towards the outside of the spiral.

As the outer spiral already is somewhat outside the substrate, it would have been interesting to see how this N. chamberlaini would finish the spiral at that point.

An egg spiral will never look the same again...

Locality: Anilao, about 15 meter, Philippines, 29 December 2008. Length: about 10 cm. Photographer: Marcel Tanke.

Best regards,
Marcel

marceltanke@cs.com

Tanke, M.A., 2009 (Sep 15) Nembrotha chamberlaini: The ART of laying eggs. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22657

Dear Marcel,

Thanks for your observations. It is indeed amazing how such an apparently clumsy organ - such as a slug's foot can lay a spiral with such precision.

I think this is the first egg ribbon I have seen of this species. It is very similar to that of Nembrotha lineolata [see message #4740]. While two species can have very similar egg ribbons, I must say that I am not convinced that all the named species of Nembrotha are different. If you imagined the brown regions in your N. chamberlaini being replaced with brown lines, it would look very much like N. lineolata.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Sep 15). Comment on Nembrotha chamberlaini: The ART of laying eggs by Marcel Tanke. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22657

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