Question

Classification of phylum porifera is based on
a. Nutrition
b. Spicules
c. Locomotion
d. Reproduction

Answer 1

Hint: Phylum Porifera are popularly known as sponges (pore bearing animals). These organisms have the body composed of many minute pores. Almost all sponges possess an internal skeleton located in the mesohyl layer.

Complete answer: Porifera is the phylum composed of the sponges. They lack true tissues, have no body symmetry, and are sessile. The classification of phylum Porifera is based upon the presence and composition of spicules.

They are divided into 3 classes:
> Class: Calcarea
> Class: Hexactinellida
> Class: Demospongiae
1. Class Calcarea: The organisms present in this class have skeletons made up of calcareous spicules. Examples: Leucosolenia, Sycon.
2. Class Hexactinellida: The organisms of this class have a skeleton of siliceous spicules which have six rays. Examples, Euplectella, Hyalonema
3. Class Demospongiae: The organisms of this class have skeletons made up of spongin fibres or of sponging fibres with siliceous spicules or may be absent. Examples, Euspogia, Spongilla.

So, the answer is option b) Spicules.

Additional information:
Skeletal structures of sponges are made up of spicules and spongin fibres. Spicules are needle-like structures formed with carbonates of lime or silica. The spicules comprise the major part of the skeletal system in sponges which are secreted by special mesenchymal cells known as scleroblasts. They are in the shape of spines or rays that radiate from the centre.
According to the size, spicules are categorized into two major types: Megascleres and microscleres. Megascleres are large-sized and constitute the main supporting framework of the sponge body. Microscleres are smaller in size and occur in the mesenchyme.

Note: The invertebrates are animals that do not contain bony structures such as the cranium and vertebrae. They have some external or internal structures that protect the soft parts of their body. In invertebrates such as sponges it is made up of calcareous and siliceous spicules.