How is the mouth of planaria similar to the proboscis of Nem

Solution

Both nemerteans and planarians are invertebrates. Planarians are tubellarian flat worms and nemerteans have been called ribbon worms. Both nemerteans and planarians are acoelomates. Nemerteans have complete digestive tract and circulatory system like coelomates, but some similarities exist with planarians. Planarians have been mostly carnivorous and they do not have digestive tract and circulatory system like nemerteans and other coelomates. Eventhough nemerteans are the primitive organisms with closed circulatory system with blood vessels structurally but functionally it looks like planarians. Planarians and nemerteans both have ciliated epidermis, sense organs such as light sensitive pigment cups. Planarians have single opening digestive tract with mouth and blind ended flame bulbs for excretion through diffusion. But in nemerteans, this digestive tube have both ends possessing openings, with mouth for food taking and blind ended tube develops into end for excretion. Reproduction through fragmentation could be seen both in planarians and nemerteans. Nemerteans also have the name proboscis worms because of distinctive feature of proboscis. Nemerteans use the proboscis to capture the prey, immobilize the prey. Proboscis is a long, hollow, sticky, muscular tube which can be moved inside out. The proboscis produces toxic chemical to kill the prey. Like the nemerteans have proboscis to capture the prey, the planarians also have tube like muscular pharynx, which is the first part of digestive tube of planarians. The planarians like the proboscis of nemerteans can push its pharynx outward to catch the prey and can take back its pharynx inside once it catches its prey through the mouth. Thus the pharynx of planarians and proboscis of nemerteans have similar features.