{ Characteristics }
Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have 3 embryonic germ layers (ectoderm, mesoderm, and endoderm), bilateral symmetry, and cephalization. Although they have 3 embryonic germ layers, they are acoelomates.
Reproduction
Flatworms have two mean of reproducing. They can reproduce asexually or sexually.
Flatworms reproduce asexually through fragmentation or fission.
Since most flatworms are hermaphrodites, they can reproduce sexually through a mutual exchange of sperm. The eggs are laid in clusters and hatch within a couple weeks.
Examples of Flatworms
There are three classes of flatworms: Turbellarians, Trematoda, and Cestoda. Turbellarians are free-living flatworms that mostly live in marine or fresh water. The most familiar are the planarians, the “cross-eyed” freshwater flatworms. Trematoda are known as flukes - parasitic flatworms that infect the internal organs of their host. The Schistosoma fluke causes schistosomiasis, a serious disease in which the eggs clog blood vessels, causing swelling and tissue decay in the lungs, liver, spleen, or intestines. The Cestoda - tapeworms - are long, flat, parasitic flatworms that are adapted to life inside the intestines of their hosts.
Vocabulary
acoelomate - without coelom
coelom - a fluid-filled body cavity that is lined with tissue derive from mesoderm
pharynx - muscular tube at the end of the gastrovascular cavity, or throat, that connects the mouth with the rest of the digestive tract and serves as a passageway for air and food
flame cell -specialized cell that filters and removes excess water from the body of a flatworm
ganglion - group of nerve cells
eyespot - group of cells that can detect changes in the amount of light in the environment
hermaphrodite - individual that has both male and female reproductive organs
fission - form of asexual reproduction in which an organism splits in two, and each half grows new parts to become a complete organism
scolex - head of an adult tapeworm; can contain suckers or hooks
proglottid - one of the segments that make up most of a tapeworm’s body
testis - male gonad that produces sperm
Works Cited
http://edu.glogster.com/media/5/24/43/95/24439576.jpg
http://www.sciencephoto.com/image/121403/530wm/C0057852-The_Fluke_Schistosoma_mansoni_-SPL.jpg
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