Question

What are Platyhelminthes (which organisms)? What are they known to be significant for in terms of animal evolution? What are their eyespots used for? Can they see well out of them?

Answer 1

Platyhelminthes or flatworms are a group of bilaterally symmetrical, acoelomate, soft-bodied invertebrate animals with no specialized cirulatory or respiratory organs with a single opening into the digestive cavity. They are found in marine, freshwater as well as moist terrestrial environment. Platyhelminthes are a rich source of evolutionary innovation. Flatworms are a group of animals that developed 3 germ layers: ectoderm, mesoderm and endoderm in contrast to diploblasts (such as cnidarians) who had 2 germ layers. This appearance of additional germ layer marks a major evolutionary advance between platyhelminthes and lower invertebrates. Flatworms have an incredible ability to regenerate the lost body part even after they have been decapitated. The platyhelminthes have two lenseless primitive eyespots on their heads that can detect the intensity of light. The eyespots are lenless, they can't see images but can sense whether it is darkness or light. Since flatworms often live in dark watery environment, the sensing of light by eyespots helps them to move away from light. No, flatworms can't see well out of the eyespot. They have lenseless and primitive eyespots which does not form images but help them to sense light intensity.