1)planaria , insects,octopus and vertebrates all have eyes.can we group these animals together to establish s common revolutionary origin?justify your answer
2)planaria , insects,octopus and vertebrates all have eyes.can these animals be grouped together on the basis of the eye they posses.why or why not
please answer me for the both queries
i am confused
give me the apt answer to scoree full marks in the upcoming board exams!

Asked by my3shyll | 12th Mar, 2017, 08:02: PM

Expert Answer:

  • Presence or development of eyes cannot be considered as a criteria 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 Playhelminthes. Random changes created a depression in the light-sensitive patch making the vision sharper in animls like planarians.
  • In insects, the light-sensitive spot gradually evolved into special layer with structures like ommatidia.
  • Later, over a period of time, 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 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 belongs to a different phyla. Therefore, it would not be possible to group these organisms together just on the basis of 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.

Answered by Sheetal Kolte | 14th Mar, 2017, 11:31: AM