1. Phylum Platyhelminthes
Areal Sutherland pd.2A

2. General Characteristics
Usually flattened dorsoventrally, triploblastic, acoelomate,
bilaterally symmetrical
Incomplete gut usually present; gut absent in Cestoidea. Somewhat cephalized, with an anterior cerebral ganglion and usually longitudinal nerve cords
Some lack digestive cavity characteristics while others have digestive tracts that are lobed. The turbellarian pharynx functions as an ingestive organ and varies in structure.
Lack respiratory organs
Carnivores or herbivores; feeding on small live invertebrates or algae. Food digestion is partly extracellular but completed as in intracellular process.
Free-living and parasitic
Asexual and sexual
Marine and terrestial

3. Other important info..
The phylum divided into four different classes: Turbellaria, Monogenea, Trematoda, Cestoidea
Over 20,000 species total
This is the first phylum covered that has an organ-system level of organization- a significant evolutionary advancement over the tissue level of organization.

4. Evolutionary Theories
One interpretation is that the triploblastic acoelomate body plan is an important intermediate between the radial, diploblastic plan and the triploblastic coelomate plan. The flatworms would thus represent an evolutionary side branch from a hypothetical triploblastic acoelomate ancestor evolution from radial ancestors could have involved a larval stage that became a sexually mature in its larval body form.
Other zoologists envision the evolution of the triploblastic, acoelomate plan from a bilateral ancestor. Primitive acoelomates, similar to flatworms, would have preceded the radiate phyla, and the radial, diploblastic plan would be secondarily derived.

5. Major classifications
Phylum Platyhelminthes-flatworms; bilateral acoelomates. Over 20,000 species
Class Turbellaria*- mostly free-living and aquatic; external surface usually ciliated; predaceous; possess rhabdites, prostrusible proboscis, frontal glands and many mucous glands: mostly hermaphroditic, convoluta, notoplana, dugesia. Over 3,000 species
Class Monogenea- monogenetic flukes; mostly ectoparasites on vertebrates; one life-cycle form in only one host; bear opisthaptor. Disocotyle, gyrodactylus, polystoma. About 1,100 species.
Class Trematoda- trematodes; all are parasitic; several holdfast devices present; have complicated life cycles involving both sexual and asexual reproduction. Over 10,000 species.
Subclass Aspidogastrea- mostly endoparasites of molluscs; possess large opisthaptor; most lack an oral sucker.aspidogaster, cotylaspis, multicotyl. About 32 species.
Subclass Digenea- adults endoparasites in vertebrates; at least two different life-cycle forms in two or more host; have oral sucker and acetabulum. Schistosoma, fasciola, clonorchis. About 1,350 species.
Class Cestoidea-all parasitic with no digestive tract; have great reproductive potential; tapeworms. About 3,500 species.
Subclass Cestodaria-body not subdivided into proglottids; larva in crustaceans, adult in fishes. Amphilina, gyrocotyle. About 15 species.
Subclass Eucestoda-true tapeworms; body divided intoscolex, neck, and strobila; strobila composed of many proglottids; both male and female reproductive systems in each proglottid; adults in digestive tract of vertebrates. Protocephalus, tainia, echinoccus, taeniarhynchus, diphyllobothrium. About 1,000 species

6. Zoology (Miller/Harley, 2005) chapter 10
Works cited
Zoology (Miller/Harley, 2005) chapter 10