Adaptations to the Environment

Flatworms:
Flat Body: Because of its flat shape, these unsegmented worms don't depend on respiratory systems; instead they can diffuse nutrients and essential gases along the body walls.
Flame Cells: some fresh-water flatworms contain flame cells, which help expel water from the body. The cells can join to form a network that empties through tiny pores in the animal's skin.
Nervous System/Brain: They have a definite head with a simple brain and developed nervous system.
-gather information from environment:
-locate food
-find dark hiding places beneath stones and logs during the day(avoid predators)
Ocelli: some have 1/more pairs of eyes spots; detect whether animal is in light or darkness. Help sense surroundings, and obtain food.
Cells: Often scattered all over body; specialized cells sensitive to chemicals found in food, and others that can tell which way the water is flowing surrounding the animal.
Muscle Cells: allow to twist and turn; able to react to environmental conditions rapidly.

Roundworms:
Simple nervous system: contains sense organs which detect chemicals given off by prey/hosts
Nerves(ganglia): transmit sensory information and control movement.