question_answer

Which type of cells is absent in sponges?

A)                  Trophocytes                     

B)  Myocytes

C)                  Archaeocytes                  

D)  Cnidocytes

Correct Answer: D

Solution :

                 Cnidocytes or stinging cells are found in entire epidermis except that of basal disc and are found only in cnidarians. These are spherical or oval cells which possess a unique type of large and centrally located sac-like organelle called nematocyst. A basal nucleus, a small Golgi complex, scattered mitochondria, ribosomes, endoplasmic reticulum and some fat globules are found in cytoplasm.                   Archaeocytes are undifferentiated totipotant cells which may differentiate into all other types of cells. Myocytes are long and slender, highly contractile spindle shaped cells resembling unstriped muscle fibres. These form a circular sphincter arround the osculum and serve to close or open it, as required. Trophocytes serve to supply nutrients to developing cells and hence, also called nurse cells.