Phylum Platyhelminthes

Characteristics of Platyhelminths

• triploblastic

• acoelomate

• dorsoventrally flattened shape

• diffusion → have micro villi to help

• some degree of cephalization evident in the free living species

• cilia for locomotion

• asexual → Budding, strobilation

• sexual → simultaneous impregnation

Class Tubellaria

• free-living predators/scavengers

• eversible pharynx

• triclad

• significant degree of cephalization

• flame cells - ciliated cells for osmoregulation and excretion

• gas exchange through diffusion

• simple nervous system

• locomotion by cilia and muscular contractions

reproduction of tubellaria

• binary fission

• simultaneous hermaphroditism

Class Cestoda

• no cephalization

• endoparasites tapeworms → infect mammals/fish

• scolex with a rostellum equipped with hooks and suckers

• dorsoventrally flattened → absorption by diffusion

• tegument → protects from acid/enzymes

• each segment is called a proglottid

  • release egg sacs → other potential hosts can take them up

Proglottids

• strobilation produces different segments

• self-fertilize

  • sperm of one proglottid fertilizes the egg of another