Ynghylch

Planaria, or planarian flatworms, are thought to be very primitive creatures as they only possess a ladder-like nervous system. Historically, planaria were classified by their ‘ecotype’, or where they occurred, as there are species that live on land in terrestrial ecosystems, freshwater ecosystems, or in marine ecosystems. It is unknown how many species of planaria exist globally, although there are thought to be 12 species in the UK, alongside invasive non-native species introduced from other parts of the world.

Planaria are carnivores, feeding on a variety of smaller invertebrates such as shrimp and water fleas in aquatic habitats, or other small worms. Some larger terrestrial species eat earthworms by wrapping around them, secreting mucus to dissolve their prey.

Species may be sexual and/ or asexual. Sexual planaria are hermaphrodites, possessing both male and female organs and able to lay eggs. As a form of asexual reproduction, planaria have a fascinating ability to regenerate into two separate individuals after damage, or can attach themselves to substrate, pulling their body to cleave themselves into two parts which then regenerate.

Thousands of tiny hair-like structures on the side of planaria may beat in motion along secreted mucus for movement in water. Some land species move using body contractions in a similar way to earthworms.