8. What is an example of
freshwater flatworm? Due to
that habitat what is the
physiological problem that
these animals must solve?

Gap-fill exercise

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Platyhelminthes of freshwater,
planarias, have an environment
much more in solutes than
exterior and so present a
tendency gain water. These
then need a system
to avoid death caused by
water.

The problem solved by the
of protonephridia located
longitudinal channels in animal
body. Protonephridia ciliated cells,
the cells, that push outside
the body excretory pores.