Question

Classification of Porifera is based up on
A. Spicules
B. Canal system
C. Amoebocytes
D. Nutrition

Answer 1

Hint: Phylum Porifera (porous bearing animals) are popularly known as sponges. The body of these species consists of several minute pores. There is an internal skeleton found in the mesohyl layer in almost all sponges. The phylum Porifera, which is composed of three distinct classes, is divided into approximately 5,000 living sponge species.

Complete answer:
Porifera is a phylum which is made up of sponges. They lack true tissues, have no symmetry with the body, and are sessile. Sponges are made up of spicules and spongin fibers in the skeletal structures of sponges. Spicules are needle-like structures made of lime or silica carbonate. Poriferans are diploblastic and have ectoderm and endoderm layers with two germs. Spongin fibers and spicules are made up of the internal skeleton. The structural elements present in most sponges are spicules. The classification of the phylum Porifera is based on the occurrence of spicules and their composition. They are split into three categories: Class: Calcarea, Hexactinellida, Demospongiae.
1. Class Calcarea: Skeletons made up of calcareous spicules belong to the species found in this class. Examples: Sycon, Leucosolenia.
2. Class Hexactinellida: The species in this class have a six-ray skeleton of silica spicules. E.g., Euplectella, Hyalonema.
3. Class Demospongiae: Organisms in this class have, or maybe missing, skeletons composed of spongin fibers or spongin fibers with silica spicules. E.g., Euspongia, Spongilla.
Hence, the correct answer is Option A.

Note: Animals that do not contain bony structures such as the cranium and vertebrae are invertebrates. They have some external or internal structures that shield their body's soft parts. It consists of calcareous and silica spicules in invertebrates such as sponges.