Photoreceptors of the earthworm occur on their:
Correct answer: C. Dorsal surface
- A. Clitellum
- B. Many eyes
- C. Dorsal surface
- D. Lateral sides
Explanation
Photoreceptors are restricted only to the dorsal surface. They are more numerous on the prostomium and peristomium of the earthworm and gradually reduce in number towards the posterior end of the body. They are totally absent in the clitellum. Each photoreceptor consists of a single ovoid cell, with a nucleus and clear cytoplasm containing a network of neurofibrillae and a small transparent L shaped lens or optic organelle made up of a hyaline substance. Photoreceptors enable worms to judge the intensity and duration of light.
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About Kingdom Animalia
Animals are multicellular, heterotrophic eukaryotes whose cells lack cell walls and chloroplasts, with specialised tissues in most groups. Coverage includes body symmetry, tissue layers, coelom, segmentation and levels of organisation, plus major phyla such as Porifera, Cnidaria, Platyhelminthes, Annelida, Arthropoda, Mollusca and Chordata.
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