Question

Spicules and amoebocytes in a sponge occur in its
A. Pinacoderm
B. Choanoderm
C. Mesenchyma
D. Spongocoel

Answer 1

Hint: Pinacoderm and choanoderm are the outermost and innermost layers of sponges covering the hollow spongocoel. They are made of pinacocytes and choanocytes respectively.

Complete answer:
The correct answer is C.
Sponges are a clade belonging to the phylum porifera. They are distinguished organisms with numerous characteristic pores on the entries body, called ostia, which facilitate flow of water through and into the spongocoel, (a large cavity centrally placed in sponges) and outside.
They have a large opening at the top, called an osculum via which the water along with waste products is ejected.
Sponges have a simple basic form of three layering. There is an innermost thin layer of choanocytes, cylindrical cells that line the spongocoel. These cells possess flagella with direct water through the sponges’ body into the spongocoel. This layer is called choanoderm. The outermost layer is constituted by Pinacocytes. These cells form the outer skin of sponges and also help digest material into smaller size. Between the outer pinacoderm and innermost choanoderm lies the mesohyl.
Mesohyl is a jelly-like matrix filling the space between pinacoderm and choanoderm entirely. Mesohyl is composed of various essential cells and elements like collagen, amoebocytes, galectin, and various polypeptides and skeletal constituents.
Amoebocytes are unspecialised cells that are capable of transforming into diverse types of cells. Other than the cellular contents, mesohyl also has a non cellular region composed of fibrils and spicules that provide mechanical and structural support to the organism.

Note: Mesohyl bears a resemblance to mesenchymal and was also known as mesenchymal. It is the only gelatinous region that contains all the diverse cellular parts. Pinacoderm and choanoderm are just thin cellular layers whereas spongocoel is a hollow central tube.