The correct answer is A. Scleroblasts.
Scleroblasts are the cells in poriferans that secrete the skeleton. They are found in the mesohyl, which is the jelly-like substance that fills the body of a sponge. Scleroblasts secrete a variety of materials, including calcium carbonate, silica, and spongin. These materials form the skeleton of the sponge, which provides support and protection.
Collenocytes are cells that produce collagen. Collagen is a protein that is found in the connective tissue of animals. It is a strong, flexible material that helps to hold the body together. Archaeocytes are stem cells that can differentiate into any type of cell in the body. Pinacocytes are cells that form the outer layer of the sponge. They are flat cells that are connected to each other by tight junctions.
Scleroblasts are the only cells in poriferans that secrete the skeleton. The other cells in poriferans have different functions. Collenocytes produce collagen, archaeocytes are stem cells, and pinacocytes form the outer layer of the sponge.