Question

Assertion: Spongilla and Leucosolenia are not placed in the same order.
Reason: In Spongilla the body is flattened or rounded, whereas in Leucosolenia it is radially symmetrical.
A. Both Assertion and reason are correct and reason is the correct explanation for assertion.
B. Both Assertion and reason are correct but reason is not the correct explanation for assertion.
C. Assertion is correct but the reason is incorrect.
D. Assertion is incorrect but the reason is correct.

Answer 1

Porifera is the lowest phylum of multicellular organisms in the kingdom animalia. The pore bearers or pore bearing animals are referred to as “Porifera”. There are approximately $5000$ species in this phylum. They are the first multicellular organisms with pores. Ostia is the name for the pores. The poriferans are called sponges because they have a spongy texture. They are immobile since they are bound to the substratum. They have the ability to absorb as well as retain fluids.

Complete explanation:
Option A:
Spongilla is a genus of freshwater sponges belonging to the class Haplosclerida. Leucosolenia is a calcareous sponge genus that belongs to the Leucosolenia family and order Leucosolenia. Spongilla is an asymmetrical freshwater sponge, while Leucosolenia is cylindrical, with radial symmetry.
Option A is incorrect.
Option B:
Spongilla is a genus of freshwater sponges belonging to the class Haplosclerida that can be found in lakes and sluggish streams. Leucosolenia is a calcareous sponge genus that belongs to the Leucosoleniidae family and order Leucosolenida. The body of Spongilla is flattened or rounded, while the body of Leucosolenia is radially symmetrical.
So, option B is correct.
Option C:
Leucosolenia is a colonial sponge that is exclusively marine, sessile, and radially symmetrical. Spongilla is a genus of freshwater sponges in the spongillidae family.
So, option C is incorrect.
Option D:
Both Spongilla and Leucosolenia belong to the phylum Porifera. Spongilla belongs to the Haplosclerida class of Demospongia, while Leucosolenia belongs to the Asconosa class of Calcarea. Spongilla is an asymmetrical freshwater sponge, while Leucosolenia is a cylindrical, white or dull grey-coloured individual with radial symmetry.
So, option D is incorrect.

So, Option B is the correct answer.

Note:
Spongilla is a genus of freshwater sponges belonging to the Spongillidae family that can be found in lakes, rivers, and slow-moving streams. Sponges of the genus Spongilla cling to rocks, logs, and even the shore, filtering the water for protozoans, bacteria, and other free-floating pond life. Leucosolenia is a calcareous sponge genus that belongs to the Leucosoleniidae family. This genus' species are commonly found in groups of curved vases that are up to $2cm$ long and end in an osculum. Leucosolenia is a marine colonial sponge that is sessile and radially symmetrical.