Elysia timida from the French Mediterranean [3]

Dear Dom,

I guess when you say teeth you are talking about the black spots along the edge of the upper lip. They certainly look like little black spikes but in your side-on view in the photo alongside you can see that the edge of the lips are not white, but have a translucent-transparent edge, and the black specks are embedded in that.

Sacoglossans, like Elysia, are characterised by a special form of the mollusc radula in which there is a single row of teeth, each tooth usually being the shape of a knife blade or dagger, which they use for piercing a hole in the cell wall of their plant food so they can suck out the cell contents. The radula teeth of molluscs is on a tongue-like ribbon rather than part of a pair of biting jaws like us.

Which brings us back to the black things. I have no idea what they are. Having a look at one of Arnaldo Marin's papers (1993) in which he describes the development of the larvae, he says that newly hatched juveniles 'progressively develop black epidermal pigment which covers the head .. tip of rhinophore rudiments and the oral lobes...' I can't see any mention about when they lose this black pigment, but I suspect your mystery black specks are the remains of this black pigment. Hopefully someone can help us

• Marin, A. and Ros, J. (1993) Ultrastructural and ecological aspects of the development of chloroplast retention in the sacoglossan gastropod Elysia timida. Journal of Molluscan Studies 59: 95-104.
• Marin, A. and Ros, J. D. ( 1989) The chloroplast-animal association in four Iberian Sacoglossan Opisthobranchs: Elysia timida, Elysia translucens, Thuridilla hopei and Bosellia mimetica. Scientia Marina 53: 429-440.
  Marin, A. and Ros, J. D. ( 1992) Dynamics of a peculiar plant-herbivore relationship: the phtosynthetic ascoglossan Elysia timida and the chlorophycean Acetabularia acetabulum. Marine Biology 112: 677-682, Figs 1-10.

Best wishes,
Bill Rudman