**Core Concept**
The intestinal amebae are a group of protozoa that infect the human intestine, causing diseases such as amoebiasis. They are characterized by their ability to invade the intestinal mucosa and form cysts.

**Why the Correct Answer is Right**
Intestinal amebae, specifically Entamoeba histolytica, invade the intestinal mucosa by producing proteolytic enzymes that break down the mucin layer and the basement membrane. This allows them to penetrate the epithelial cells and form cysts. The cysts are highly resistant to environmental changes and can be transmitted through contaminated food or water.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the intestinal amebae. While some amebae may be free-living, intestinal amebae are specifically adapted to infect the human intestine.

**Option B:** This option is incorrect because it does not mention the invasive properties of intestinal amebae. While some amebae may cause diarrhea, the intestinal amebae are known for their ability to invade the intestinal mucosa.

**Option C:** This option is incorrect because it does not accurately describe the life cycle of intestinal amebae. While cysts are an important stage in the life cycle of some amebae, the intestinal amebae are specifically known for their ability to invade the intestinal mucosa and form cysts.

**Clinical Pearl / High-Yield Fact**
The intestinal amebae can be diagnosed through the examination of stool samples, which may reveal the presence of cysts or trophozoites. A key feature of intestinal amebiasis is the presence of dysentery, which is characterized by bloody diarrhea and abdominal pain.

**Correct Answer:** C.