Question

Which of the features is not shown by sponges?
A) Sponges lack tissue and body symmetry
B) Sponges belong to the phylum Porifera
C) Sponges are mainly found in marine habitats, but some may also be found in freshwater
D) Swimming is possible for the sponge larvae as they have cilia.

Answer 1

Hint: Sponges are primitive multicellular animals. About 5000 species of sponges are known. They are called ‘pore bearers’ as their body walls possess numerous tiny pores. They are sessile and remain attached to the ground with the help of an object called substratum.

Complete answer:
Sponges belong to the phylum Porifera. They are aquatic and most of them are marine but few sponges live in freshwater also. For example, sapodilla is a freshwater sponge, found in lakes and slow streams.
 Most of them are asymmetric as any plane passing through their body centre cannot divide them into equal halves. They have a cellular level of organisation. These cells cannot form tissues. All cells. Division of labour is present among the cells but act more or less independently and show little coordination.

There are no respiratory structures in the sponges so the exchange of $O_2$ and $CO_2$ occurs through the water entering and going out with the help of a canal system. Sponges are filter feeders as the microvilli of collar cells filter the microscopic plants and animals from the water entering the body. These food particles are then taken up by the choanocytes for intracellular digestion. The development of an adult sponge from a diploid zygote is indirect, which means it is mediated by free-swimming flagellated larvae stages for dispersal of species.

Thus the correct answer is option ‘D’ i.e, because, larvae do not swim because of cilia.

Note: Sexual reproduction occurs by the formation of haploid male and female gametes. The sperms leave the body of one sponge and enter that of another with the water current to fertilise the ovum in situ condition.