April 8, 2003
From: Rachel Przeslawski
I recently collected a bunch of Codium with these Elysia species (E. maoria?) all over it. When brought back to the lab they laid several of these odd looking egg masses which seem identical to the one we looked at when you were last at University of Wollongong. They're normal sacoglossan flattened spirals, but they have what appear to be evenly spaced yolk granules on top of the mass. This isn't too unusual as Boucher (1983) has documented this before. What's odd is that some of the yolk granules appear to be smaller and completely black; these could be a completely different structure than the yolk, but I just can't imagine what! Any ideas?
Przeslawski, R., 2003 (Apr 8) Elysia maoria(?) and egg masses. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/9583
Yes this is the egg mass we looked at previously. I suspected it was that of Elysia maoria, but at that time we didn't have an animal to confirm the identification. Concerning the mystery 'yolk' objects. I thought I had seen them before. They were described by Jocelyn Reid (1964) in her study of E. maoria in New Zealand. Although she gives a detailed description of the workings of the reproductive system, she doesn't say much about the mystery objects - just calls them 'pockets of granular secretion'. They don't look like the extra-capsular yolk which some opisthobranchs produce, and which has been reviewed, as you mention, by Boucher (1983). Extra-capsular yolk is usually in streaks, or a long string, outside the egg capsule, but within the envelope of the egg ribbon - presumably so it's accessible to the developing larvae. In this egg ribbon the 'yolk' capsules seem to be outside the layer enclosing the egg ribbon.
A similar egg ribbon has been reported in a few other sacoglossans. There are photos in the Forum of the egg ribbon of Elysia gordanae and Thuridilla vatae with identical strutures, and Ortea, Luque & Templado (1988) describe similar egg ribbons from the Canary Ids for Thuridilla picta and Bosellia leve. They identify it as extra-capsular yolk. Species of Thuridilla are all thought to have extra-capsular yolk [see Kathe Jensen's message] but as I say above, in some instances it is an internal thread. It would be interesting to have other observations and thoughts on this.
• Boucher, L. M. (1983) Extra-capsular yolk bodies in the egg masses of some tropical Opisthobranchia. Journal of Molluscan Studies, 49(3): 232-241.
• Ortea, J.A., Luque, A.A. & Templado, J. (1988) Elysia picta Verrill, 1901, and Geitodoris pusae (Marcus, 1955), two amphiatlantic opisthobranch gastropods. J. Moll. Stud., 54: 243-247.
• Reid, J.D. (1964) The reproduction of the ascoglossan opisthobranch Elysia maoria. Proceedings of the Zoological Society, London, 143(3): 365-393.