Introduction to the PlatyhelminthesLife in two dimensions. . .

•The simplest animals that are bilaterally symmetrical and composed of three fundamental cell layers

•Acoelomate= FLAT!

•Lack an anus, the same pharyngeal opening both takes in food and expels waste

•first creature to develop a head, brain, paired senses and a tail, the first to move forward and thus the first to hunt for food and mates

•20,000 kinds of flatworms are alive and well today

•fresh and salt-water environments and other nice damp niches, like the insides of other animals.

•Fossil Record: Platyhelminths have practically no fossil record (except eggs)

Platyhelminthes Taxonomy1.Turbellaria- mostly free-living, includes the

planarian (e.g. Dugesia), these are found in the oceans, in fresh water, and in moist terrestrial habitats, and a few are parasitic.

2.Trematoda- flukes, all parasitic, and have complex life cycles specialized for parasitism in animal tissues. Members of one major taxon of flukes, the Digenea, Schistosoma -- which includes the human lung fluke

3.Cestoda- tapeworms (Taenia), are intestinal parasites in vertebrates, and they also show anatomical and life history modifications for parasitism

Review of Morphology of Common Flatworm

•Bilaterally symmetrical with a head and a tail •Centralized nervous system •Three tissue layers •No body cavity, no circulatory system and no hard skeleton•Colored (e.g. marine flatworms)•With eyespot

Flatworms have both male and female sex organs in the one animal. If you think about it, that's a great way to be. If you're rare and you're looking for a mate and you're traveling alone, you don't have to meet another female or another male. You just have to meet another one. -- Leslie Newman

Philippine FlatwormsArea: Malapascua Island, Philippines

Pseudoceros sp.

Philippine FlatwormsArea: Cebu Island, Moalboal, Philippines

Maritigrella sp.

Pseudoceros sp.

Pseudoceros sp.

Philippine FlatwormsArea: Puerto Galera, Philippines

Pseudoceros sp.

Philippine FlatwormsArea: Batangas, Philippines

Pseudoceros sp.

Cycloporus sp.

Pseudoceros sp.

Class Trematoda•The image is a fluke (possibly a species of Probolitrema). Flukes, like other parasitic flatworms, have complex life cycles often involving two or more host organisms.

•Lung Fluke