Question

Which of the following gives the most appropriate meaning of choanocytes?
A. Reproductive cells
B. Nutritive cells
C. Spicule forming cells
D. Excretory cells

Answer 1

Choanocytes cells are seen mainly in the sponge belonging to the phylum Porifera. The choanocyte cells form a layer which is also known as the inner endoderm, it is the innermost layer of the sponge. Spongocoel (internal sponge cavity discharging by the way of the osculum) and the lines of canals are lined by the flagellated collar cells called choanocytes.

Complete answer:
Choanocytes are the specialized containing a single flagellum surrounded by net-like collar microvilli, they are joined together in the innermost layer of the sponge, where they perform two major functions one of which is the creation of the flow of water and the second is capturing of the food items that pass by these cells.
A sponge can reproduce both sexually and asexually, asexually it reproduces by budding, fission, and gemmule formation and sexual reproduction occurs by gamete formation. No specialized reproductive organs or cells are seen. Hence the option A. Reproductive cell is incorrect.
The walls of the endoderm, pinacoderm and endoderm are separated by the means of gelatinous mesenchyme provided with spicules (which can be calcareous, silicious, sponging fiber-containing), these act as the structural component. Hence the option C. Spicule forming cells is incorrect.
The process of excretion is performed by the Ostia. Hence the option D. Excretory cell is incorrect.

The choanocytes are mainly used for the catching of prey and act as a nutritive cell. Hence the option B. Nutritive cell is correct.

Note. :
Based on spicules the sponges can be classified– a. Calcarea (calcareous spicules. It includes Leucosolenia), b. Hexactinellida or Hyalospongiae (Siliceous spicules. It includes Euplectella) and c. Demospongiae (Siliceous spicules containing or have sponging fibers or can have both things). Spongilla is the best example. Sponges are known as filter feeders.