Final answer:
Acoel flatworms lack a coelom, some have no digestive system (such as tapeworms), but they do have a simplified nervous system. They possess bilateral symmetry and evolved features like a muscular and excretory system, despite the absence of circulatory and respiratory systems.
Step-by-step explanation:
The correct characteristics of acoel flatworms are:
- Lack of a coelom
- Absence of a digestive system (in tapeworms)
- Presence of a nervous system
Flatworms are known for having bilateral symmetry and are classified as acoelomates because they do not have a true body cavity. Although flatworms lack a circulatory and respiratory system, they do have an incomplete digestive system, except for tapeworms which do not have a digestive system at all. The nervous system in flatworms is quite simple, characterized by a ladder-like structure with two interconnected parallel nerve cords and a pair of cerebral ganglia in the head region, which play a role in sensory functions.
It's important to note that while flatworms lack complex systems seen in other organisms, they have evolved certain features such as a muscular system for movement and an excretory system to maintain fluid and electrolyte balance. Therefore, the correct options that describe acoel flatworms are their lack of body symmetry, absence of a coelom, and presence of a nervous system.