we see eyes in planaria, insects, octopus, and vertebrates
can eye be grouped together in case of above mentioned animals to establish a common evolutionary origin. why?
Answers
no because the eye in planaria is just two spots but in insects it is used for seeing.
hence it cannot be used for classification
Presence or development of eyes cannot be considered as a criterion for classification of animals. It is, in fact, an important feature which has been favoured in the history of evolution.
The early design of rudimentary eyes in the form of eye-spots was observed in Planaria which belongs to phylum Platyhelminthes. Random changes created a depression in the light-sensitive patch making the vision sharper in animals like planarians.
In insects, the light-sensitive spot gradually evolved into a special layer with structures like ommatidia.
Later, over a period of time, the lens was formed in front of the eye.Vertebrates and octopuses developed the eye resembling a pin-hole camera wherein nerve fibres passed in front of the retina.
Cephalopods have eyes in which nerves are attached to the retina. They do not have a blind spot. Blind spot is present in the retina of the vertebrate eye whereas blind spot is absent in the octopus eye.
This eye design has gone through many changes and complexities to form the human eye. Human eye is a complex structure made up of different structures which individually are incapable of vision.
Thus, we can see that structure of eyes in each of these organisms is different suggesting a separate evolutionary origin.
Insects, octopus planaria are invertebrates.They do not have a backbone which is a characteristic of vertebrates.Moreover, each of these organisms belong to different phyla. Therefore, it would not be possible to group these organisms together just on the basis of the presence of eyes. We need to have a broader basis and a set of different criteria such as cellularity, type of food, symmetry, body plan, etc. for their classification.