Zooplanktonic forms are c) primary consumers.
Explanation: Zooplankton are small, often microscopic animals that drift in water. They play a crucial role in aquatic food webs by feeding on phytoplankton, which are the primary producers in these ecosystems. As they consume phytoplankton, zooplankton convert this energy into a form that can be utilized by higher trophic levels, including fish and other carnivores. Thus, they are categorized as primary consumers rather than primary producers or carnivores.