Flatworms also have a feature that the sponges and cnidarians do not, a middle layer of actual organized cells. Flatworms have three cell layers: an ectoderm, an outer covering like the other groups have; an endoderm, a lining of the digestive spaces somewhat like a cnidarians; and a mesoderm between the other two. With actual tissues protected like this, another evolutionary explosion of features happened.
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Mertztown, PA Other Information. 1  Located in BERKS County, Pennsylvania. 2  Mertztown, PA is also known as: 3  DRYVILLE, PA.  FREDERICKSVILLE, 1  PA. HANCOCK, 2  PA. KLINES CORNER, 3  PA. LONGSWAMP,  PA. LOWER 1  LONGSWAMP, PA. OREVILLE,  PA. SHAMROCK STATION, PA.