Solar-powered Flatworms...Convoluta

March 2, 1999
From: Snow

Dr. Rudman,

I have a couple questions about Convoluta:
1. Is photosynthesis the only way thru which it captures energy?
2.Does it consume anything else? What's with the eating egg-case thing?
3.How exactly does it sense the tidal changes?

I tried surfing the net, it was no good help. This forum seems to have the answers. Thanx a lot!!


Huang, S., 1999 (Mar 2) Solar-powered Flatworms...Convoluta. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Snow,
I'm afraid I don't know much about flatworms. The Forum is for people interested in sea slugs. However I guess the species of Convoluta you are interested in is Convoluta roscoffensis or one of the other species which have symbiotic algae in their tissues.

Most modern reports say that Convoluta roscoffensis needs the algal cells (Platymonas convoluta) to survive. The algae cells inside the worm are rounded and hardly look like an algal cell. However when they are released into the sea water the quickly change shape and swim to nearby flatworm eggs where they burrow inside the eggs and grow and multiply inside the developing flatworm embryo. Another species, Convoluta paradoxa is thought to have photosynthetic diatoms in its tissues.

On sheltered sandy beaches France and parts of England they form great green streaks across the sand at low tide. Some years ago in tropical East Africa I used to find a species that lived at a particular level on sandy shores there. If you put them in a glass tube (or jar) with sand, and wrapped the sides with black paper you could see how they reponded to changes in light intensity. If you moved a light up and down above the jar the flatworms would form a green band in the sand which sank deeper in the sand as the light got closer and rose towards the surface of th sand as you moved the light away. Clearly they preferred a certain level of light intensity. I guess in the tropics such worms have to be able to adjust the amount of light they receive so their plants don't get burnt out by too much light.

I don't know what you mean by eating the "egg case thing". There is one very old reference which says that the algae live in the coccoon which encases the flatworm eggs before they hatch. When the flatworms hatch they engulf the algae and so get them inside their bodies. Is that what you are referring to? I don't know how they sense the tidal changes.

I have listed a couple of references below, but you would need to go to a University or Museum library to find them.

Best wishes,
Bill Rudman.

* Holligan,PM & Gooday, GW. (1977) Symbiosis in Convoluta roscoffensis. Symposia of the Society of experimental Biology, 29(1975): 205-227.
* Douglas, AE. (1983) Establishment of the symbiosis in Convoluta roscoffensis. Journal of the marine Biological association, United Kingdom, 63: 409-418.

Rudman, W.B., 1999 (Mar 2). Comment on Solar-powered Flatworms...Convoluta by Snow. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from



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