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Sponges with skeleton of only spongin fibres occur in
A. Calcarea
B. Demospongiae
C. Hexactinellida
D. All the above

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Last updated date: 20th Jun 2024
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Answer
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Hint: Sponges are the members of phylum Porifera. Sponges are the multicellular organisms.

Complete Answer:
- The bodies of sponges are full of pores and channels that allow the water to circulate through them.
- The branch of zoology that studies sponges is called Spongiology.
- Sponges do not have nervous, digestive or circulatory systems.
- They rely on constant water flow through their bodies to obtain food and oxygen and remove wastes.
- Sponges are the firstly evolved animals.
- Calcarea, Demospongiae, Hexactinellida all three are the classes of phylum Porifera.

Sponges of class Calcarea:
- The calcareous sponges are the cellular sponges.
- They are characterized by the presence of skeletal spicules which are made up of calcium carbonate.
- These spicules protrude through the covering of the body wall and give the organism a rough texture.
- All sponges in this class are marine.

Sponges of class Demospongiae:
- Demospongiae is the most diverse class of the phylum Porifera.
- They are the sponges with a soft body that covers a hard skeleton made up of calcium carbonate.
- Their skeletons are made up of spicules which consist of the sponging fibre, or mineral silica.
 Example – Aplysina , Niphates, etc.

Sponges of class Hexactinellida:
- The sponges of class Hexactinellida are also called glass sponges.
- They are deep sea sponges.
They are the sponges with a skeleton made of four or six pointed siliceous spicules.
 Example – Eupllectella
Therefore, it is clear that the sponges with a skeleton of only sponging fibres occur in class Demospongiae.

Hence, option B is the correct answer for this question.

Note: Sea sponges can be used in the health and beauty field. These sponges have many minute pores so they can store water.