Give the characteristics of the phylum $Platyhelminthes$.

(N/A) The phylum $Platyhelminthes$ (flatworms) exhibits the following characteristics:
$1$. Body Symmetry: They are $bilaterally$ symmetrical.
$2$. Germ Layers: They are $triploblastic$ (three germ layers: ectoderm, mesoderm, and endoderm).
$3$. Body Cavity: They are $acoelomate$ (lack a true body cavity).
$4$. Organization: They show $organ-system$ level of body organization.
$5$. Digestive System: The digestive system is incomplete (a single opening serves as both mouth and anus).
$6$. Excretion: Specialized cells called $flame$ cells (protonephridia) help in osmoregulation and excretion.
$7$. Reproduction: They are mostly $hermaphrodite$ (bisexual). Fertilization is internal, and development includes many larval stages.
$8$. Lifestyle: Many members are endoparasites in animals, including humans. They possess hooks and suckers for attachment.