Phylum Platyhelmenthes (the flatworms) General characteristics

Phylum Platyhelmenthes (the flatworms)General characteristics

Eumetazoa - animals with tissue– Bilateria - have bilateral symmetry

Head end-cephalization

Tail end

Right and left side

Top (dorsal) and bottom (ventral)

triploblastic -ectoderm, mesoderm, endoderm.

Protostomia - a group of animals whose mouth develops from the blastopore, and the mesoderm forms from an area near the blastopore.

Acoelomata - They have a true mesoderm which fills the original blastocoel between the outer epidermis and digestive tract.

IntegumentaryIntegumentary- Rhabdites and one cell layer epidermis in Turbellaria and usually ciliated; syncytial tegument in other classes.

SkeletalSkeletal - hydrostatic

MuscleMuscle - longitudinal, transverse, and circular muscles are present.

DigestiveDigestive - incomplete with intracellular and extracellular digestion; no system in Cestoda.

Excretory Excretory - flame cells, or excretory tubes in Cestoda.

RespiratoryRespiratory - no system, diffusion

CirculatoryCirculatory - none, diffusion.

NervousNervous - anterior ganglia, ventral ladder-like system (two lateral cords with transverse cords).

a bilobed anterior ganglial mass (brain)

Protonephridia-a series of flame cells that aid in excretion

Endocrine Endocrine - hormones produced by nervous system

ReproductiveReproductive - monoecious in mostWell developed reproductive organs, mostly

internal fertilization.Two of the parasitic classes have complex life

cyclesTrematoda -Cestoda -

Class Turbellaria-~5000 species, mostly free-living~Dugesia- free living planarian

Branched gut

Reproduction- asexual- fission sexual - monoecious

Diversity-land planarian- Bipalium

Gone fission

Branched guteyespots

Class Trematoda--flukes~parasitic

endoparasiticectoparasitic

~tegument=body wall~suckers~feed on host cells, tissue fluids, mucus (yuk!) and blood

~life cyclemonogenic flukesdigenic flukes

Opisthorchis - Human liver fluke

Schistosoma --- swimmer’s itch

Class Cestoda = tapeworms

Proglottids-Head-scolex

proglottidScolex

Proglottid- note interconnection

Scolex

Life cycle

Phylum Nemertina- ribbon worms

Proboscis can be extruded to capture food

General characteristics-~tube within a tube body plan- a complete digestive tract

~Acoelomate

~eversible proboscis, within a rhinocoel above the gut

~feeding-stylets and toxins

~closed circulator system, a single dorsal vessel with two lateral vessels

~paired lateral longitudinal nerve cords

~asexual reproduction by fragmentation~sexual reproduction-

dioeciousfree-swimming larva in some marine species

Advanced Features-~anus~closed circulatory system~dorsal nerve cord in some~complex excretory system in close association with circulatory system~mesodermally derived blood vessels & mesodermally lined

rhinocoel may provide links to higher phyla