Planarian Flatworms
Our primary model organism for studying regeneration
Meet the Planarian
Planarians are non-parasitic members of the class Turbellaria (phylum Platyhelminthes). There are thousands of species — they live in lakes and rivers, the ocean, and even on land. We use freshwater species for the ease of care. We keep them at room temperature, in the dark (as they are photophobic), in plain mineral water, in tupperware containers. They have a single opening through which they extend their pharynx, or feeding tube, to eat (see video above). In the lab, we feed our planarians liver pâté that we make especially for them.
Life in the Lab
Planarian colony containers
Pharynx extension during feeding
Species We Study
We use mainly two species in the lab: Schmidtea mediterranea, which has a sequenced genome and for which there exist both an obligate asexual strain and a sexual strain (planarians are hermaphroditic); and Dugesia japonica, which are larger and hardier and perfectly suited to chemical genetic screens.
Additionally, for our evolutionary research, we also keep small colonies of several other planarian species. As you can see in the image, they come in a wide range of colors, sizes, and head shapes. One species, Polycelis felina, even has 20–30 eye spots.
This natural variation in body morphology is one of the reasons planarians are great for studying how animal shape is re-established during regeneration — all of our planarian species are regenerative.
Regeneration: The Superpower
Planarians are a powerful regeneration model because they can reproduce asexually, by transverse fissioning. During fissioning, worms basically attach themselves by their tail and then stretch until they pull themselves apart! The head fragment regenerates a new tail, and the tail fragment regenerates a new head — and 7–14 days later, you have two genetically identical worms.
Planarians can do this remarkable feat because roughly 25% of their body is made up of adult stem cells, able to regenerate all tissues. In the lab, we utilize this ability to further our understanding of regeneration (see image).
