The nervous system is derived from
All of the above: it depends on whether the animal is a protostome or a deuterostome
Planarians lack dedicated respiratory and circulatory systems because
none of their cells are far removed from the gastrovascular cavity or from the external environment.
they lack mesoderm as embryos and therefore lack the adult tissues derived from mesoderm.
their flame bulbs can carry out respiratory and circulatory functions.
their pseudocoelom carries out these functions.
Animals with bilateral symmetry
can be divided into similar halves by any plane through the longitudinal axis.
are usually very slow-moving organisms.
are relatively simple in structure.
are better adapted for forward movement than radially symmetrical organisms.
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