Question

Which of the following statements is correct for sponges without exception?
A. They all have calcareous spicules.
B. They have high regenerative power.
C. They are found only in marine water.
D. They are all radially symmetrical.

Answer 1

Hint: Sponges belong to the phylum: Porifera. The word Porifera stands for pore bearing. There are numerous pores on the surface of the sponge bodies which are known as the Ostia which leads into the anastomosing canal, all of these canals open into a central cavity known as spongocoel which further opens through a terminally large opening known as the osculum.

Complete answer:
The regenerative power of all the sponges is very high and no exception is seen. Hence option B is the correct option.
The spicules are present in the gelatinous mesenchyme between the layers of the outer ectoderm and the inner endoderm. The spicules can be of three types in the sponges.
Calcareous spicules : Found in the class: Calcarea . Example: Scypha
Siliceous spicules: Found in the class: Hexactinellida. Example: Euplectella
Siliceous spicules or spongin fibers or both: Found in class: Demospongiae. Example: spongilla
Hence the option A . contains an exception and hence it is incorrect.

Sponges are mostly marine but some sponges are freshwater living also. It includes Spongilla.
Hence exceptions are seen. Hence the option C is incorrect.

Sponges are not only radially symmetrical but also they can be asymmetrical. Hence option D is incorrect.

Note:
The respiratory, excretory, and nervous systems are absent in the case of sponge. They reproduce in both sexual and asexual mode, sexually by gamete formation and asexually by budding, fission, or gemmule formation. They are hermaphrodites in nature but cross-fertilization is not seen. No definite mouth or alimentary canal is seen, they are filter feeders.