TP - The flatworm of Roscoff, an illustration of biodiversity

Extract from the Official Bulletin:
Second - Earth in the Universe, life and the evolution of living beings: an inhabited planet.
Biodiversity, a result and stage of evolution.

Scientific issue:
The Flatworm of Roscoff or Symsagittifera roscoffensis is a photosymbiotic flatworm.
Its particularity lies in its ability to live with a microalgae, Tetraselmis convolutae, which gives it photosynthetic activity.
Studying the Roscoff Flatworm can allow students to make observations and measurements to identify some aspects of biodiversity.
Thus, during evolution, certain associations between living beings have occurred, some of which are visible today.
The concept of biodiversity, a result of evolution, can then be illustrated using an original example.

Operational procedure:
Observing the Roscoff Flatworm (binocular loupe, optical microscope) reveals the presence of a large number of green particles which are actually microalgae. Studying the worm's metabolism shows that in sequences of "darkness - light" type, the animal performs both respiratory and photosynthetic activities.