Question:
Insects,octopus,planaria and vertebrates posseses eyes. Can we group these animals together on the basis of the eyes they possess
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.
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