Final answer:
The eusporangium is the type of sporangium with a thick wall that is several layers thick, providing protection for developing spores and aiding in their survival. The correct option is a.
Step-by-step explanation:
The type of sporangium that possesses a thick wall several layers thick is known as eusporangium. This structure contrasts with a leptosporangium, which typically has a thinner wall made up of a single layer of cells.
In the context of spore development, the thick wall of the eusporangium provides protection and helps in the survival of the spores under various environmental conditions. An example of a structure with a thick, protective coat is the zygosporangium, which results from the fusion of + and - mating types and contains multiple haploid nuclei.
The thick cell walls of such structures usually contain a tough polymer called sporopollenin, which is highly resistant to degradation and is also found in pollen grains of seed plants. The correct option is a.