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.
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Phylum Platyhelmenthes (the flatworms)
Eumetazoa - animals with tissue
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.
Integumentary- Rhabdites and one cell layer epidermis in Turbellaria and usually ciliated; syncytial tegument in other classes.
Skeletal - hydrostatic
Muscle - longitudinal, transverse, and circular muscles are present.
Digestive - incomplete with intracellular and extracellular digestion; no system in Cestoda.
Excretory - flame cells, or excretory tubes in Cestoda.
Respiratory - no system, diffusion
Circulatory - none, diffusion.
Nervous - 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 - hormones produced by nervous system
Reproductive - monoecious in most
Well developed reproductive organs, mostly internal fertilization.
Two of the parasitic classes have complex life cycles
~5000 species, mostly free-living
~Dugesia- free living planarian
sexual - monoecious
Diversity-land planarian- Bipalium
~feed on host cells, tissue fluids, mucus (yuk!) and blood
Opisthorchis - Human liver fluke
Schistosoma --- swimmer’s itch
Class Cestoda = tapeworms
Proglottid- note interconnection
Phylum Nemertina- ribbon worms
Proboscis can be extruded to capture food
~tube within a tube body plan- a complete digestive tract
~eversible proboscis, within a rhinocoel above the gut
~feeding-stylets and toxins
~closed circulator system, a single dorsal vessel with two lateral
~paired lateral longitudinal nerve cords
~asexual reproduction by fragmentation
free-swimming larva in some marine species
~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